Engineered immunostimulatory bacterial strains and uses thereof

ABSTRACT

Provided are delivery immunostimulatory bacteria that have enhanced colonization of tumors, the tumor microenvironment and/or tumor-resident immune cells, and enhanced anti-tumor activity. The immunostimulatory bacteria are modified by deletion of genes encoding the flagella or modification of the genes so that functional flagella are not produced, and/or are modified by deletion of pagP or modification of pagP to produce inactive PagP product. As a result, the immunostimulatory bacteria are flagellin− and/or pagP−. The immunostimulatory bacteria optionally have additional genomic modifications so that the bacteria are adenosine or purine auxotrophs. The bacteria optionally are one or more of asd−, purI− and msbB−. The immunostimulatory bacteria, such as Salmonella species, are modified to encode immunostimulatory proteins that confer anti-tumor activity in the tumor microenvironment, and/or are modified so that the bacteria preferentially infect immune cells in the tumor microenvironment or tumor-resident immune cells and/or induce less cell death in immune cells than in other cells. Also provided are methods of inhibiting the growth or reducing the volume of a solid tumor by administering the immunostimulatory bacteria.

RELATED APPLICATIONS

This application is a continuation of International PCT Application No. PCT/US2019/041489, filed on Jul. 11, 2019, to Applicant Actym Therapeutics, Inc., inventors Christopher D. Thanos, Laura Hix Glickman, Justin Skoble and Alexandre Charles Michel Iannello, and entitled “Engineered Immunostimulatory Bacterial Strains and Uses Thereof.” International PCT Application No. PCT/US2019/041489 claims the benefit of priority to U.S. Provisional Application Ser. No. 62/789,983, filed on Jan. 8, 2019, to Applicant Actym Therapeutics, Inc., inventors Christopher D. Thanos, Laura Hix Glickman, Justin Skoble and Alexandre Charles Michel Iannello, and entitled “Engineered Immunostimulatory Bacterial Strains and Uses Thereof,” and to U.S. Provisional Application Ser. No. 62/828,990, filed on Apr. 3, 2019, to Applicant Actym Therapeutics, Inc., inventors Christopher D. Thanos, Laura Hix Glickman, Justin Skoble and Alexandre Charles Michel Iannello, and entitled “Salmonella Strains Engineered To Colonize Tumors And The Tumor Microenvironment.”

Benefit of priority also is claimed to U.S. Provisional Application Ser. No. 62/789,983, filed on Jan. 8, 2019, to Applicant Actym Therapeutics, Inc., inventors Christopher D. Thanos, Laura Hix Glickman, Justin Skoble and Alexandre Charles Michel Iannello, and entitled “Engineered Immunostimulatory Bacterial Strains and Uses Thereof.”

Benefit of priority also is claimed to U.S. Provisional Application Ser. No. 62/828,990, filed on Apr. 3, 2019, to Applicant Actym Therapeutics, Inc., inventors Christopher D. Thanos, Laura Hix Glickman, Justin Skoble and Alexandre Charles Michel Iannello, and entitled “Salmonella Strains Engineered To Colonize Tumors And The Tumor Microenvironment.”

The immunostimulatory bacteria provided in each of these applications can be modified as described in this application and such bacteria are incorporated by reference herein. The subject matter of each of these applications is incorporated by reference in its entirety.

INCORPORATION BY REFERENCE OF SEQUENCE LISTING PROVIDED ELECTRONICALLY

An electronic version of the Sequence Listing is filed herewith, the contents of which are incorporated by reference in their entirety. The electronic file was created on Jul. 17, 2019, is 457 kilobytes in size, and is titled 1704SEQ001.txt.

FIELD OF THE INVENTION

Provided are immunostimulatory bacteria with genomes that are modified to, for example, increase colonization of the tumor microenvironment, tumors, and/or tumor-resident immune cells. This increase in colonization improves delivery of encoded therapeutic products and permits systemic administration of the immunostimulatory bacteria.

BACKGROUND

The field of cancer immunotherapy has made great strides, as evidenced by the clinical successes of anti-CTLA4, anti-PD-1 and anti-PD-L1 immune checkpoint antibodies (see, e.g., Buchbinder et al. (2015) J. Clin. Invest. 125: 3377-3383; Hodi et al. (2010) N. Engl. J. Med. 363(8):711-723; and Chen et al. (2015) J. Clin. Invest. 125:3384-3391). Tumors have evolved a profoundly immunosuppressive environment. They initiate numerous mechanisms to evade immune surveillance, reprogram anti-tumor immune cells to suppress immunity, and continually mutate resistance to the latest cancer therapies (see, e.g., Mahoney et al. (2015) Nat. Rev. Drug Discov. 14(8):561-584). Designing immunotherapies that overcome immune tolerance and escape, while limiting the autoimmune-related toxicities of current immunotherapies, challenges the field of immuno-oncology. Hence, additional and innovative immunotherapies and other therapies are needed.

SUMMARY

Provided are bacteria modified to be immunostimulatory for anti-cancer therapy. Immunostimulatory bacteria, as provided herein, provide a multi-faceted approach to anti-tumor therapy. Bacteria provide a platform in which there are numerous avenues for eliciting anti-tumor immunostimulatory activity. As provided herein, bacteria, such as species of Salmonella, are fine-tuned to have potent anti-tumor activity by increasing their ability to accumulate in or target tumors, tumor-resident-immune cells, and/or the tumor microenvironment (TME). This is achieved by modifications that, for example, alter the type of cells that they can infect (tropism), their toxicity, their ability to escape the immune system, such as complement, and/or the environments in which they can replicate. The immunostimulatory bacteria also can encode, for example, products that enhance or invoke an immune response, and therapeutic products. The immunostimulatory bacteria provided herein, by virtue of their improved colonization of tumors, the tumor microenvironment, and/or tumor-resident immune cells, and their resistance to complement and other anti-bacterial immune responses, can be administered systemically.

The genomes of the bacteria provided herein are modified to increase accumulation in tumors and in tumor-resident immune cells, and also in the tumor microenvironment. This is effected herein by deleting or disabling genes responsible for infection or invasion of non-tumor cells, such as epithelial cells, and/or decreasing the cytopathogenicity of the bacteria, particularly to immune cells and tumor-resident immune cells.

Bacteria by their nature stimulate the immune system; bacterial infection induces immune and inflammatory pathways and responses, some of which are desirable for anti-tumor treatment, and others, are undesirable. Modification of the bacteria by deleting or modifying genes and products that result in undesirable inflammatory responses, and adding or modifying genes and products that induce desirable immunostimulatory anti-tumor responses, improves the anti-tumor activity of the bacteria.

Bacteria accumulate in tumor cells and tissues, and by replicating therein, can lyse cells. Bacteria migrate from the sites of administration and can accumulate in other tumors and tumor cells to provide an abscopal effect. The bacteria provided herein are modified so that they preferentially infect and accumulate in tumor-resident immune cells, tumors, and the tumor microenvironment.

Herein, all of these properties of bacteria are exploited to produce demonstrably immunostimulatory bacteria with a plurality of anti-tumor activities and properties that can act individually and synergistically.

Provided are compositions, uses thereof and methods that modulate immune responses for the treatment of diseases, including for the treatment of cancer. The compositions contain immunostimulatory bacteria provided herein. Methods of treatment and uses of the bacteria for treatment also are provided. The subjects for treatment include humans and other primates, pets, such as dogs and cats, and other animals, such as horses.

Provided are pharmaceutical compositions containing the immunostimulatory bacteria, and methods and uses thereof for treatment of diseases and disorders, particularly proliferative disorders, such as tumors, including solid tumors and hematologic malignancies.

Also provided are methods of inhibiting the growth or reducing the volume of a solid tumor by administering the immunostimulatory bacteria or pharmaceutical compositions, or using the compositions for treatment. For example, provided are methods of administering or using a composition that contains, for a single dosage, an effective amount of an attenuated Salmonella species to a subject, such as a human patient, having a solid tumor cancer. It is understood that all modifications to the genome of the bacteria, such as anti-tumor therapeutics, and other modifications of the bacterial genome and the plasmids described, can be combined in any desired combination.

Provided are immunostimulatory bacteria that have enhanced colonization of tumors, the tumor microenvironment and/or tumor-resident immune cells, and enhanced anti-tumor activity. The immunostimulatory bacteria are modified by deletion of genes encoding the flagella, or modification of the genes so that functional flagella are not produced, and/or deletion of pagP or modification of pagP to produce inactive PagP product. As a result, the immunostimulatory bacteria are flagellin⁻ (fliC⁻/fljB⁻) and/or pagP⁻. Alternatively, or additionally, the immunostimulatory bacteria can be pagP⁻/msbB⁻.

The immunostimulatory bacteria can be flagellin deficient, such as by deletion of, or disruption in, a gene(s) encoding the flagella. For example, provided are immunostimulatory bacteria that contain deletions in the genes encoding one or both of flagellin subunits fliC and fljB, whereby the bacterium is flagella deficient, and wherein the wild-type bacterium expresses flagella. The immunostimulatory bacteria also can have a deletion or modification in the gene encoding endonuclease I (endA), whereby endA activity is inhibited or eliminated.

The immunostimulatory bacteria optionally have additional genomic modifications so that the bacteria are adenosine or purine auxotrophs. The bacteria optionally are one or more of asd⁻, purI⁻ and msbB⁻. The immunostimulatory bacteria, such as Salmonella species, are modified to encode immunostimulatory proteins that confer anti-tumor activity in the tumor microenvironment, and/or are modified so that the bacteria preferentially infect immune cells in the tumor microenvironment or tumor-resident immune cells, and/or induce less cell death in immune cells than in other cells. Also provided are methods of inhibiting the growth or reducing the volume of a solid tumor by administering the immunostimulatory bacteria.

Provided are methods of increasing tumor colonization of an immunostimulatory bacterium, such as a Salmonella species, by modifying the genome of the immunostimulatory bacterium to be flagellin⁻ (fliC⁻/fljB⁻) and/or pagP⁻.

The bacteria also contain plasmids that encode therapeutic products, such as anti-tumor agents, proteins that increase the immune response of a subject, and inhibitory RNA (RNAi) that target immune checkpoints. For example, the plasmids can encode immunostimulatory proteins, such as cytokines, chemokines, and co-stimulatory molecules, that increase the anti-tumor response in the subject. The bacteria contain plasmids that encode anti-cancer therapeutics, such as RNA, including microRNA, shRNA, and siRNA, and antibodies and antigen-binding fragments thereof that are designed to suppress, inhibit, disrupt or otherwise silence immune checkpoint genes and products, and other targets that play a role in pathways that are immunosuppressive. The bacteria also can encode tumor antigens and tumor neoantigens on the plasmids to stimulate the immune response against the tumors. The encoded proteins are expressed under the control of promoters recognized by eukaryotic, such as mammalian and animal, or viral, transcription machinery.

Provided are immunostimulatory bacteria that contain a plasmid encoding a therapeutic product, such as an anti-cancer therapeutic; the genome of the immunostimulatory bacterium is modified so that it preferentially infects tumor-resident immune cells and/or so that it induces less cell death in tumor-resident immune cells.

Provided are immunostimulatory bacteria containing a plasmid encoding a product, generally a therapeutic product, such as an anti-cancer therapeutic product, under control of a eukaryotic promoter, where the genome of the immunostimulatory bacterium is modified whereby the bacterium is flagellin⁻ (fliC⁻/fljB⁻) and/or pagP⁻, and whereby the wild-type bacteria have flagella. The bacteria can be one or both of flagellin⁻ (fliC⁻/fljB⁻) and pagP⁻. These immunostimulatory bacteria exhibit increased colonization of tumors, the tumor microenvironment and/or tumor-resident immune cells, and have increased anti-tumor activity.

Among these immunostimulatory bacteria are those that are flagellin⁻ (fliC⁻/fljB⁻), and whereby the therapeutic product is an anti-cancer product. In some embodiments, the bacteria are flagellin⁻ (fliC⁻/fljB⁻), and the product is an anti-cancer therapeutic protein or nucleic acid.

Among these immunostimulatory bacteria are those in which the therapeutic product is a TGF-beta antagonist polypeptide, where the genome of the immunostimulatory bacterium is modified so that the bacterium preferentially infects tumor-resident immune cells, and/or the genome of the immunostimulatory bacterium is modified so that it induces less cell death in tumor-resident immune cells (decreases pyroptosis), whereby the immunostimulatory bacterium accumulates in tumors or in the tumor microenvironment or in tumor-resident immune cells to thereby deliver the TGF-beta antagonist polypeptide to the tumor microenvironment. The TGF-beta antagonist can be selected from among an anti-TGF-beta antibody, an anti-TGF-beta receptor antibody, and a soluble TGF-beta antagonist polypeptide. The nucleic acid encoding the TGF-beta antagonist polypeptide can include nucleic acid encoding a signal sequence for secretion of the encoded polypeptide, so that it is released into the tumor cells, tumor-resident immune cells, and/or the tumor microenvironment.

In other embodiments of any of the immunostimulatory bacteria provided herein, the plasmid encodes an immunostimulatory protein that confers, enhances, or contributes to an anti-tumor immune response in the tumor microenvironment. Exemplary of immunostimulatory proteins that confer or contribute to anti-tumor immunity in the tumor microenvironment is/are one or more of: IL-2, IL-7, IL-12p70 (IL-12p40+IL-12p35), IL-15, IL-36 gamma, IL-2 that has attenuated binding to IL-2Ra, IL-15/IL-15R alpha chain complex, IL-18, IL-21, IL-23, IL-36γ, IL-2 modified so that it does not bind to IL-2Ra, CXCL9, CXCL10, CXCL11, interferon-α, interferon-β, interferon-γ, CCL3, CCL4, CCL5, proteins that are involved in or that effect or potentiate recruitment/persistence of T cells, CD40, CD40 ligand (CD40L), CD28, OX40, OX40 ligand (OX40L), 4-1BB, 4-1BB ligand (4-1BBL), members of the B7-CD28 family, CD47 antagonists, TGF-beta polypeptide antagonists, and members of the tumor necrosis factor receptor (TNFR) superfamily.

In other embodiments of the immunostimulatory bacteria provided herein, the therapeutic product is an antibody or antigen-binding fragment thereof. Exemplary of such is a Fab, Fab′, F(ab′)₂, single-chain Fv (scFv), Fv, disulfide-stabilized Fv (dsFv), nanobody, diabody fragment, or a single-chain antibody. The antibody or antigen-binding fragment thereof can be humanized or human. Exemplary of an antibody or antigen-binding fragment thereof is an antagonist of PD-1, PD-L1, CTLA-4, VEGF, VEGFR2, or IL-6.

The immunostimulatory bacteria provided herein, including those described above, can contain a plasmid encoding a therapeutic product under control of a eukaryotic promoter; the genome of the immunostimulatory bacterium is modified whereby the bacterium is pagP⁻/msbB⁻, and optionally flagellin⁻ (fliC⁻/fljB⁻).

Exemplary of immunostimulatory bacteria are those that contain a plasmid encoding an immunostimulatory protein, where: an immunostimulatory protein, when expressed in a mammalian subject, confers or contributes to anti-tumor immunity in the tumor microenvironment; the immunostimulatory protein is encoded on a plasmid in the bacterium under control of a eukaryotic promoter; and the genome of the immunostimulatory bacterium is modified so that it preferentially infects tumor-resident immune cells. In other embodiments, the immunostimulatory bacteria contain a sequence of nucleotides encoding an immunostimulatory protein, where the immunostimulatory protein, when expressed in a mammalian subject, confers or contributes to anti-tumor immunity in the tumor microenvironment; the immunostimulatory protein is encoded on a plasmid in the bacterium under control of a eukaryotic promoter; and the genome of the immunostimulatory bacterium is modified so that it induces less cell death in tumor-resident immune cells. Exemplary immunostimulatory proteins include cytokines and chemokines, and other immune stimulatory proteins, such as, for example one or more of: IL-2, IL-7, IL-12p70 (IL-12p40+IL-12p35), IL-15, IL-36 gamma, IL-2 that has attenuated binding to IL-2Ra, IL-15/IL-15R alpha chain complex, IL-18, IL-21, IL-23, IL-36γ, IL-2 modified so that it does not bind to IL-2Ra, CXCL9, CXCL10, CXCL11, interferon-α, interferon-β, interferon-γ, CCL3, CCL4, CCL5, proteins that are involved in or that effect or potentiate recruitment/persistence of T cells, CD40, CD40 ligand, CD28, OX40, OX40 ligand, 4-1BB, 4-1BB ligand, members of the B7-CD28 family, CD47 antagonists, TGF-beta polypeptide antagonists, and members of the tumor necrosis factor receptor (TNFR) superfamily.

These immunostimulatory bacteria can include modification(s) in the genomes of the immunostimulatory bacteria so that the bacteria exhibit one or both of preferentially infecting tumor-resident immune cells, and inducing less cell death in tumor-resident immune cells. The immunostimulatory bacteria can also include a mutation in the genome that reduces toxicity or infectivity of non-immune cells in a host.

Modifications of the bacterial genome include pagP⁻, or pagP⁻ and flagellin⁻ (fliC⁻/fljB⁻). In other embodiments, the immunostimulatory bacteria is one or more of purI⁻ (purM⁻), msbB⁻, purD⁻, flagellin⁻ (fliC⁻/fljB⁻), pagP⁻, adrA⁻, csgD⁻, qseC⁻, and hilA⁻, such as flagellin⁻ (fliC⁻/fljB⁻)/pagP⁻/msbB⁻/purI⁻, or flagellin⁻ (fliC⁻/fljB⁻)/pagP⁻/msbB⁻/purI⁻/hilA⁻. In other embodiments, the immunostimulatory bacteria are hilA⁻ and/or flagellin⁻ (fliC⁻/fljB⁻) or pagP⁻ or pagP⁻/msbB⁻ or the immunostimulatory bacteria are hilA⁻ or the immunostimulatory bacteria are flagellin⁻ (fliC⁻/fljB⁻) and pagP⁻. The genome modifications, among other properties, can increase targeting to or colonization of the tumor microenvironment and/or tumor-resident immune cells, and/or render the bacteria substantially or completely resistant to inactivation by complement. These properties improve the use of the bacteria as therapeutics, and permit systemic administration.

In the immunostimulatory bacteria provided herein, the nucleic acid encoding the therapeutic product is operatively linked for expression to a nucleic acid encoding a secretory signal, whereby, upon expression in a host, the immunostimulatory protein is secreted. The therapeutic product can be a protein, such as an immunostimulatory protein, or a nucleic acid, such as a CRISPR cassette or an RNAi.

In all embodiments, the immunostimulatory bacteria can be auxotrophic for adenosine, or for adenosine and adenine. The immunostimulatory bacteria provided herein can include modifications in the genome whereby the bacterium preferentially infects tumor-resident immune cells, and/or the genome of the immunostimulatory bacterium is modified so that it induces less cell death in tumor-resident immune cells (decreases pyroptosis), whereby the immunostimulatory bacterium accumulates in tumors or in the tumor microenvironment or in tumor-resident immune cells to thereby deliver an encoded therapeutic product.

In the immunostimulatory bacteria, the plasmid encodes the therapeutic product under control of a eukaryotic promoter so that it is expressed in a eukaryotic host, such as a human or other mammal. The therapeutic product generally is an anti-cancer therapeutic, such as an anti-cancer therapeutic protein that stimulates the immune system of the host. Other therapeutic products include antibodies and antigen-binding fragments thereof, and nucleic acids, such as RNAi. These products can be designed to inhibit, suppress, or disrupt a target, such as an immune checkpoint and other such targets that impair the ability of the immune system of a subject to recognize the tumor cells.

The unmodified immunostimulatory bacteria can be a wild-type strain or an attenuated strain. The genome modifications provided and described herein attenuate the bacteria outside of the tumor microenvironment or tumors; the modifications, among other properties, alter the infectivity of the bacteria. Exemplary of bacteria that can be modified as described herein is Salmonella, such as a Salmonella typhimurium strain. Exemplary of Salmonella typhimurium strains are attenuated and wild-type strains, such as, for example, Salmonella typhimurium strains derived from strains designated as AST-100, VNP20009, YS1646 (ATCC #202165), RE88, SL7207, χ8429, χ8431, χ8468, or a wild-type strain with ATCC accession no. 14028.

As discussed above, provided are immunostimulatory bacteria containing a plasmid encoding a product under control of a eukaryotic promoter, where the genome of the immunostimulatory bacterium is modified whereby the bacterium is pagP⁻/msbB⁻. Deletion of msbB alters the acyl composition of the lipid A domain of lipopolysaccharide (LPS), the major component of the outer membranes of Gram-negative bacteria, such that the bacteria predominantly produce penta-acylated LPS instead of the more toxic and pro-inflammatory hexa-acylated LPS. In wild type S. typhimurium, expression of pagP results in hepta-acylated lipid A, while in an msbB⁻ mutant, the induction of pagP results in hexa-acylated LPS. Thus, a pagP⁻/msbB⁻ mutant produces only penta-acylated LPS, resulting in lower induction of pro-inflammatory cytokines, and enhanced tolerability, which allows for higher dosing in humans. Higher dosing leads to increased colonization of tumors, tumor-resident immune cells, and the tumor microenvironment. Because of the resulting change in bacterial membranes and structure, the host immune response, such as complement activity, is altered so that the bacteria are not eliminated upon systemic administration. For example, it is shown herein that pagP/msbB⁻ mutant strains have increased resistance to complement inactivation and enhanced stability in human serum. These bacteria also can be flagellin⁻ (fliC⁻/fljB⁻), which further enhances tolerability, resistance to complement inactivation, and tumor/TME/tumor-resident immune cell colonization. The bacteria also can comprise other modifications as described herein, including modifications that alter the cells that they can infect, resulting in accumulation in the tumor microenvironment, tumors and tumor-resident immune cells. Hence, the immunostimulatory bacteria provided herein can be systemically administered and exhibit a high level of tumor, tumor microenvironment and/or tumor-resident immune cell colonization. The immunostimulatory bacteria can be purI⁻ (purM⁻), and one or more of asd⁻, msbB⁻, and one or both of flagellin⁻ (fliC⁻/fljB⁻) and pagP⁻.

The immunostimulatory bacteria can be aspartate-semialdehyde dehydrogenase⁻ (asd⁻), such as by virtue of disruption or deletion of all or a portion of the endogenous gene encoding aspartate-semialdehyde dehydrogenase (asd), whereby endogenous asd is not expressed. These immunostimulatory bacteria can be modified to encode aspartate-semialdehyde dehydrogenase (asd) on a plasmid under control of a bacterial promoter so that the bacteria can be produced in vitro.

The immunostimulatory bacteria can be rendered auxotrophic for particular nutrients that are rich or that accumulate in the tumor microenvironment, such as adenosine and adenine. Also, they can be modified to be auxotrophic for such nutrients to reduce or eliminate their ability to replicate. The inactivated/deleted bacterial genome genes can be complemented by providing them on a plasmid under the control of promoters recognized by the host.

The products encoded on the plasmids for expression in a eukaryotic, such as a human, host, are under control of eukaryotic regulatory sequences, including eukaryotic promoters, such as promoters recognized by RNA polymerase II or III. These include mammalian RNA polymerase II promoters. Viral promoters also can be used. Exemplary viral promoters, include, but are not limited to, a cytomegalovirus (CMV) promoter, an SV40 promoter, an Epstein Barr virus (EBV) promoter, a herpes virus promoter, and an adenovirus promoter. Other RNA polymerase II promoters include, but are not limited to, an elongation factor-1 (EF1) alpha promoter, a UbC promoter (lentivirus), a PGK (3-phosphoglycerate kinase) promoter, and a synthetic promoter such as a CAGG (or CAG) promoter. The synthetic CAG promoter contains the cytomegalovirus (CMV) early enhancer element (C); the promoter, the first exon and the first intron of chicken beta-actin gene (A); and the splice acceptor of the rabbit beta-globin gene (G). Other strong regulatable or constitutive promoters can be used. The regulatory sequences also include terminators, enhancers, and secretory and other trafficking signals.

The plasmids included in the immunostimulatory bacteria can be present in low copy number or medium copy number, such as by selection of an origin of replication that results in medium-to-low copy number, such as a low copy number origin of replication. It is shown herein that the anti-tumor activity and other properties of the bacteria are improved when the plasmid is present in low to medium copy number, where medium copy number is less than 150 or less than about 150 and more than 20 or about 20 or is between 20 or 25 and 150 copies, and low copy number is less than 25 or less than 20 or less than about 25 or less than about 20 copies.

These immunostimulatory bacteria can be modified so that the bacteria preferentially infect tumor-resident immune cells, and/or the genome of the immunostimulatory bacteria can be modified so that they induces less cell death in tumor-resident immune cells (decrease pyroptosis), whereby the immunostimulatory bacteria accumulate in tumors or in the tumor microenvironment or in tumor-resident immune cells.

As discussed above, the genome of the immunostimulatory bacteria also is modified so that the bacteria preferentially infect immune cells, such as tumor-resident immune cells, such as myeloid cells, such as cells that are CD45⁺, and/or the genome is modified so that the bacteria induce less cell death in tumor-resident immune cells (decreased pyroptosis) than the unmodified bacteria. As a result, the immunostimulatory bacteria accumulate, or accumulate to a greater extent than those without the modifications, in tumors or in the tumor microenvironment or in tumor-resident immune cells, to thereby deliver the therapeutic product or products encoded on the plasmid. The bacteria can be one or more of flagellin⁻ (fliC⁻/fljB⁻), pagP⁻, and msbB⁻, and can include other such modifications as described herein. The bacteria can be auxotrophic for adenosine, and/or purI⁻ (purM⁻) and/or asd⁻.

The immunostimulatory bacteria provided herein can include a modification of the bacterial genome, whereby the bacteria induce less cell death in tumor-resident immune cells; and/or a modification of the bacterial genome, whereby the bacteria accumulate more effectively in tumors, the tumor microenvironment, or tumor-resident immune cells, such as tumor resident CD45⁺ cells, and myeloid cells.

For example, the immunostimulatory bacteria can include deletions or modifications of one or more genes or operons involved in SPI-1 invasion (and/or SPI-2), whereby the immunostimulatory bacteria do not invade or infect epithelial cells. Exemplary of genes that can be deleted or inactivated are one or more of avrA, hilA, hilD, invA, invB, invC, invE, invF, invG, invH, invI, invJ, iacP, iagB, spaO, spaP, spaQ, spaR, spaS, orgA, orgB, orgC, prgH, prgI, prgJ, prgK, sicA, sicP, sipA, sipB, sipC, sipD, sirC, sopB, sopD, sopE, sopE2, sprB, and sptP. Elimination of the ability to infect epithelial cells also can be achieved by engineering the immunostimulatory bacteria herein to contain knockouts or deletions of genes encoding proteins involved in SPI-1-independent invasion, such as one or more of the genes selected from among rck, pagN, hlyE, pefI, srgD, srgA, srgB, and srgC. Similarly, the immunostimulatory bacteria can include deletions in genes and/or operons in SPI-2, for example, to engineer the bacteria to escape the Salmonella-containing vacuole (SCV). These genes include, for example, sifA, sseJ, sseL, sopD2, pipB2, sseF, sseG, spvB, and steA.

The immunostimulatory bacteria provided herein also can contain a sequence of nucleotides encoding an immunostimulatory protein that, when expressed in a mammalian subject, confers or contributes to anti-tumor immunity in the tumor microenvironment; the immunostimulatory protein is encoded on a plasmid in the bacterium under control of a eukaryotic promoter. Exemplary promoters include, but are not limited to, an elongation factor-1 (EF1) alpha promoter, or a UbC promoter, or a PGK promoter, or a CAGG or CAG promoter.

Additionally, the genome of the immunostimulatory bacterium is modified so that it preferentially infects tumor-resident immune cells. This is achieved by deleting or disrupting bacterial genes that play a role in invasiveness or infectivity of the bacteria, and/or that play a role in inducing cell death. The bacteria are modified to preferentially infect tumor-resident immune cells, and/or induce less cell death in tumor-resident immune cells than in other cells that the bacteria can infect, than unmodified bacteria.

The immunostimulatory bacteria also can encode a therapeutic product, such as inhibitory RNA (RNAi), immunostimulatory proteins such as cytokines, chemokines and co-stimulatory molecules, other proteins that increase the immune response in a subject, and other anti-tumor agents, that, when expressed in a mammalian subject, confer or contribute to anti-tumor immunity. The therapeutic product is encoded on a plasmid in the bacterium under control of a eukaryotic promoter. The genome of the immunostimulatory bacterium is modified so that it induces less cell death in tumor-resident immune cells. The plasmid generally is present in low or medium copy number.

Also provided are immunostimulatory bacteria that encode an immunostimulatory protein on a plasmid in the bacterium under control of a eukaryotic promoter, that, when expressed in a mammalian subject, confers or contributes to anti-tumor immunity in the tumor microenvironment. The immunostimulatory bacteria can be modified to have reduced pathogenicity, whereby infection of epithelial and/or other non-immune cells is reduced, relative to the bacterium without the modification. These include modification of the type 3 secretion system (T3SS) or type 4 secretion system (T4SS), such as modification of the SPI-1 pathway of Salmonella as described and exemplified herein. The bacteria further can be modified to induce less cell death, such as by deletion or disruption of nucleic acid encoding lipid A palmitoyltransferase (pagP), which reduces virulence of the bacteria.

The genome of the immunostimulatory bacteria provided herein can be modified to increase or promote infection of immune cells, particularly immune cells in the tumor microenvironment, such as phagocytic cells. This includes reducing infection of non-immune cells, such as epithelial cells, or increasing infection of immune cells. The bacteria also can be modified to decrease pyroptosis in immune cells. Numerous modifications of the bacterial genome can do one or both of increasing infection of immune cells and decreasing pyroptosis. The immunostimulatory bacteria provided herein include such modifications, for example, deletions and/or disruptions of genes involved in the SPI-1 T3SS pathway, such as disruption or deletion of hilA, and/or disruption/deletion of genes encoding flagellin, rod protein (PrgJ), needle protein (PrgI) and QseC.

The immunostimulatory bacteria can be one or more of purI⁻ (purM⁻), msbB⁻, purD⁻, flagellin⁻ (fliC⁻/fljB⁻), pagP⁻, adrA⁻, csgD⁻, qseC⁻, and hilA⁻, and particularly flagellin⁻ (fliC⁻/fljB⁻) and/or pagP⁻, and/or msbB⁻/pagP⁻. For example, the immunostimulatory bacteria can include mutations in the genome, such as gene deletions or disruptions that reduce toxicity or infectivity of non-immune cells in a host. For example, the immunostimulatory bacteria can be pagP⁻. As another example, the immunostimulatory bacteria can be hilA⁻ and/or flagellin⁻ (fliC⁻/fljB⁻), and also can be pagP⁻. Thus, for example, the immunostimulatory bacteria can encode an immunostimulatory protein, such as a cytokine, and the bacteria can be modified so that they accumulate and express the cytokine in the tumor microenvironment (TME), thereby delivering an immunotherapeutic anti-tumor product into the environment in which it has beneficial activity, and avoiding adverse or toxic side effects from expression in other cells/environments. The nucleic acid encoding the immunostimulatory protein can be operatively linked for expression to nucleic acid encoding a secretory signal, whereby, upon expression in a host, the immunostimulatory protein is secreted into the tumor microenvironment.

The immunostimulatory bacteria provided herein include any of the strains and bacteria described in co-pending U.S. application Ser. No. 16/033,187, or published International Application No. PCT/US2018/041713 (published as WO 2019/014398), further modified to express an immunostimulatory protein and/or to preferentially infect and/or to be less toxic in immune cells in the tumor microenvironment or in tumor-resident immune cells, as described and exemplified herein.

The immunostimulatory bacteria can be aspartate-semialdehyde dehydrogenase⁻ (asd⁻), such as by virtue of disruption or deletion of all or a portion of the endogenous gene encoding aspartate-semialdehyde dehydrogenase (asd), whereby the endogenous asd is not expressed. The immunostimulatory bacteria can be modified to encode aspartate-semialdehyde dehydrogenase (asd) on a plasmid under control of a bacterial promoter for growing the bacteria in vitro, so that bacteria will have limited replication in vivo.

The immunostimulatory bacteria provided herein can encode, on a plasmid, an immunostimulatory protein as a therapeutic product. The immunostimulatory protein can be a cytokine, such as a chemokine, or a co-stimulatory molecule. Exemplary of immunostimulatory proteins are IL-2, IL-7, IL-12p70 (IL-12p40+IL-12p35), IL-15, IL-15/IL-15R alpha chain complex, IL-36 gamma, IL-18, CXCL9, CXCL10, CXCL11, CCL3, CCL4, CCL5, proteins that are involved in or that effect or potentiate the recruitment/persistence of T cells, CD40, CD40 Ligand (CD40L), OX40, OX40 Ligand (OX40L), 4-1BB, 4-1BB Ligand (4-1BBL), members of the B7-CD28 family, and members of the tumor necrosis factor receptor (TNFR) superfamily.

The immunostimulatory bacteria optionally can include a sequence of nucleotides encoding inhibitory RNA (RNAi) that inhibits, suppresses or disrupts expression of an immune checkpoint. The RNAi can be encoded on a plasmid in the bacterium. The nucleotides encoding the immunostimulatory protein, and optionally an RNAi, can be on a plasmid present in low to medium copy number.

The immunostimulatory bacteria also can encode therapeutic products, such as RNAi or a CRISPR cassette that inhibits, suppresses or disrupts expression of an immune checkpoint or other target whose inhibition, suppression or disruption increases the anti-tumor immune response in a subject; the RNAi or CRISPR cassette is encoded on a plasmid in the bacterium. Other therapeutic products include, for example, antibodies that bind to immune checkpoints to inhibit their activities.

RNAi includes all forms of double-stranded RNA that can be used to silence the expression of targeted nucleic acids. RNAi includes shRNA, siRNA and microRNA (miRNA). Any of these forms can be interchanged in the embodiments disclosed and described herein. In general, the RNAi is encoded on a plasmid in the bacterium. The plasmids can include other heterologous nucleic acids that encode products of interest that modulate or add activities or products to the bacterium, or other such products that can modulate the immune system of a subject to be treated with the bacterium. Bacterial genes also can be added, deleted or disrupted. These genes can encode products for growth and replication of the bacteria, or products that also modulate the immune response of the host to the bacteria.

The immunostimulatory bacteria provided herein also can be auxotrophic for adenosine, or for adenosine and adenine.

Bacterial species for modification as described herein, carrying plasmids as described herein, include, but are not limited to, for example, strains of Salmonella, Shigella, Listeria, E. coli, and Bifidobacteriae. For example, species include Shigella sonnei, Shigella flexneri, Shigella dysenteriae, Listeria monocytogenes, Salmonella typhi, Salmonella typhimurium, Salmonella gallinarum, and Salmonella enteritidis.

Species include, for example, strains of Salmonella, Shigella, E. coli, Bifidobacteriae, Rickettsia, Vibrio, Listeria, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Cholera, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Bacillus, and Erysipelothrix, or an attenuated strain thereof or a modified strain thereof of any of the preceding list of bacterial strains.

Other suitable bacterial species include Rickettsia, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Vibrio, Bacillus, and Erysipelothrix. For example, Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia tsutsugamuchi, Rickettsia mooseri, Rickettsia sibirica, Bordetella bronchiseptica, Neisseria meningitidis, Neisseria gonorrhoeae, Aeromonas eucrenophila, Aeromonas salmonicida, Francisella tularensis, Corynebacterium pseudotuberculosis, Citrobacter freundii, Chlamydia pneumoniae, Haemophilus somnus, Brucella abortus, Mycobacterium intracellulare, Legionella pneumophila, Rhodococcus equi, Pseudomonas aeruginosa, Helicobacter mustelae, Vibrio cholerae, Bacillus subtilis, Erysipelothrix rhusiopathiae, Yersinia enterocolitica, Rochalimaea quintana, and Agrobacterium tumerfacium.

Salmonella is exemplified herein, and particularly Salmonella typhimurium strains. The Salmonella can be wild-type species or attenuated species. Exemplary of some attenuated species are the strains designated YS1646 (ATCC #202165) or VNP20009. Other strains include, RE88, SL7207, χ8429, χ8431, and χ8468. Exemplary of wild-type or unattenuated species include, for example, the wild-type strain deposited as ATCC 14028, or a strain having all of the identifying characteristics of ATCC 14028. The modifications herein attenuate any strain by constraining the cells that the bacteria can infect or in which they can replicate.

These strains can be further modified to encode immunostimulatory proteins and/or immune modulatory proteins. For example, the immunostimulatory bacteria can encode immunostimulatory proteins, such as cytokines, that increase the immune response in the tumor microenvironment. The immunostimulatory bacteria also can be modified to preferentially infect immune cells in the tumor microenvironment or to infect tumor-resident immune cells, and/or to induce less cell death in such immune cells, as described herein. Sequences thereof and descriptions are provided in the detailed description, examples and sequence listing. The immunostimulatory bacteria can be derived from attenuated strains of bacteria, or they become attenuated by virtue of the modifications described herein, such as deletion of asd, whereby replication is limited in vivo.

It is understood that instances in which bacterial genes are modified and referenced herein, they are referenced with respect to their designation (name) in Salmonella species, which is exemplary of bacteria from which immunostimulatory bacteria can be produced. The skilled person recognizes that other species have corresponding proteins, but that their designation or name can be different from the name in Salmonella. The generic disclosure herein, however, can be applied to other bacterial species. For example, as shown herein, deletion or inactivation of flagellin (fliC⁻/fljB⁻) in Salmonella and/or pagP results in increased colonization of tumors. Similar genes encoding flagella, or similar functions for infection, can be modified in other bacterial species to achieve increased tumor colonization. Similarly, inactivation/deletion of bacterial products, such as the products of pagP and/or msbB, as described herein, can reduce complement activation and/or other inflammatory responses, thereby increasing targeting to tumors, tumor-resident immune cells and the tumor microenvironment. Corresponding genes in other species that are involved in activating the complement pathway or other inflammatory pathway, can be deleted, as exemplified herein for Salmonella.

The immunostimulatory bacteria provided herein encode inhibitors of various genes that reduce anti-tumor immune responses, and/or express genes and/or gene products that contribute to anti-tumor immune responses and/or products that stimulate the immune system, such as immunostimulatory proteins, such as cytokines, chemokines, and co-stimulatory molecules, and thereby are immunostimulatory. Adenosine auxotrophy is immunostimulatory. Other therapeutic products that can be encoded on the plasmids are nucleic acids, such as inhibitory RNA (RNAi), such as shRNA or microRNA or siRNA, targeted for disruption or inhibition of expression of TREX1, PD-L1, VISTA (the gene encoding V-domain Ig suppressor of T cell activation), TGF-beta, and CTNNB1 (the gene that encodes β-catenin), among others, combinations thereof, and combinations thereof with any RNAi's that inhibit, suppress or disrupt expression of other immune suppressive genes whose expression is activated or enhanced by tumors or the tumor microenvironment (TME). Expression of these RNAs exploits two independent immunostimulatory pathways, and leads to enhanced tumor colonization in a single therapy. The effects of this combination are enhanced by the strains provided herein that are auxotrophic for adenosine, which provides preferential accumulation in, or recruitment into, adenosine-rich immunosuppressive tumor microenvironments. Reducing adenosine in such TMEs further enhances the immunostimulatory effects. Such combinations of traits in any of the bacterial strains known, or that can be engineered for therapeutic administration, provide similar immunostimulatory effects.

Among the targets is TGF-beta, which has three isoforms: 1, 2 and 3. Among the targets is TGF-beta, particularly isoform 1, and not isoforms 2 and 3. Toxicities are associated with inhibition of isoforms 2 and 3. For example, cardiac valve toxicity is associated with inhibition of isoform 2. Isoform 1 is present in most cancers (see, e.g., TCGA database). It is advantageous to inhibit only isoform 1. RNAi can be advantageously employed for this purpose, since it can be designed to very specifically recognize a target. For TGF-beta, specific inhibition of isoform 1 can be effected by targeting a sequence unique to isoform 1 that is not present in isoforms 2 or 3, or to select a sequence to target isoforms 1 and 3, and not 2. Also provided are immunostimulatory bacteria in which the plasmid encodes an shRNA or microRNA that specifically inhibits, suppresses or disrupts expression of TGF-beta isoform 1 but not TGF-beta isoform 2 or TGF-beta isoform 3; or the plasmid encodes an shRNA or microRNA that specifically inhibits, suppresses or disrupts expression of TGF-beta isoforms 1 and 3, but not isoform 2.

RNAi, such a miRNA- or shRNA-mediated gene disruption of PD-L1 by the immunostimulatory bacteria provided herein, also improves colonization of tumors, the TME, and/or tumor-resident immune cells. It has been shown that knockout of PD-L1 enhances S. typhimurium infection. For example, an at least 10-fold higher bacterial load in PD-L1 knockout mice than in wild-type mice has been observed, indicating that PD-L1 is protective against S. typhimurium infection (see, e.g., Lee et al. (2010) J. Immunol. 185:2442-2449).

Engineered immunostimulatory bacteria, such as the S. typhimurium immunostimulatory bacteria provided herein, contain multiple synergistic modalities to induce immune re-activation of cold tumors to promote tumor antigen-specific immune responses, while inhibiting immune checkpoint pathways that the tumor utilizes to subvert and evade durable anti-tumor immunity. Included in embodiments is adenosine auxotrophy and enhanced vascular disruption. This improvement in tumor targeting through adenosine auxotrophy and enhanced vascular disruption increases potency, while localizing the inflammation to limit systemic cytokine exposure and the autoimmune toxicities observed with other immunotherapy modalities.

The heterologous therapeutic proteins and other products, such as the immunostimulatory proteins, antibodies, and RNAs, are expressed on plasmids under the control of promoters that are recognized by the eukaryotic host cell transcription machinery, such as RNA polymerase II (RNAP II) and RNA polymerase III (RNAP III) promoters. RNAP III promoters generally are constitutively expressed in a eukaryotic host; RNAP II promoters can be regulated. The therapeutic products are encoded on plasmids stably expressed by the bacteria. Exemplary of such bacteria are Salmonella strains, generally attenuated strains, either attenuated by passage or other methods, or by virtue of modifications described herein, such as adenosine auxotrophy. Exemplary of Salmonella strains are modified S. typhimurium strains that have a defective asd gene. These bacteria can be modified to include carrying a functional asd gene on the introduced plasmid; this maintains selection for the plasmid so that an antibiotic-based plasmid maintenance/selection system is not needed. The asd defective strains that do not contain a functional asd gene on a plasmid are autolytic in the host.

The promoters can be selected for the environment of the tumor cell, such as a promoter expressed in a tumor microenvironment (TME), a promoter expressed in hypoxic conditions, or a promoter expressed in conditions where the pH is less than 7.

Plasmids can be present in many copies or fewer. This can be controlled by selection of elements, such as the origin of replication. Low, medium and high copy number plasmids and origins of replication are well known to those of skill in the art and can be selected. In embodiments of the immunostimulatory bacteria herein, the plasmid can be present in low to medium copy number, such as about 150 or 150 and fewer copies, to low copy number, which is less than about 25 or about 20 or 25 copies. Exemplary origins of replication are those derived from pBR322, p15A, pSC101, pMB1, colE1, colE2, pPS10, R6K, R1, RK2, and pUC.

The plasmids can include RNAi such that the RNA inhibits, suppresses or disrupts expression of an immune checkpoint or other target and, additionally, their products. The plasmids also can include sequences of nucleic acids encoding a listeriolysin O (LLO) protein lacking the signal sequence (cytoLLO), a CpG motif, a DNA nuclear targeting sequence (DTS), and a retinoic acid-inducible gene-I (RIG-I) binding element. The immunostimulatory bacterium that comprises nucleic acid can include a CpG motif recognized by toll-like receptor 9 (TLR9). The CpG motif can be encoded on the plasmid. The CpG motif can be included in, or is part of, a bacterial gene that is encoded on the plasmid. For example, the gene that comprises CpGs can be asd, encoded on the plasmid. The immunostimulatory bacteria provided herein can include one or more of a CpG motif, an asd gene selectable marker for plasmid maintenance, and a DNA nuclear targeting sequence.

The immunostimulatory bacteria provided herein can encode two or more different RNA molecules that inhibit, suppress or disrupt expression of an immune checkpoint and/or an RNA molecule that encodes an inhibitor of a metabolite that is immunosuppressive or is in an immunosuppressive pathway.

The immunostimulatory bacteria provided herein can be aspartate-semialdehyde dehydrogenase⁻ (asd⁻), which permits growth in diaminopimelic acid (DAP) supplemented medium, but limits replication in vivo when administered to subjects for treatment. Such bacteria will be self-limiting, which can be advantageous for treatment. The bacterium can be asd⁻ by virtue of disruption or deletion of all or a portion of the endogenous gene encoding aspartate-semialdehyde dehydrogenase (asd), whereby the endogenous asd is not expressed. In other embodiments, the gene encoding aspartate-semialdehyde dehydrogenase can be included on the plasmid for expression in vivo.

Any of the immunostimulatory bacteria provided herein can include nucleic acid, generally on the plasmid, that includes a CpG motif or a CpG island, wherein the CpG motif is recognized by toll-like receptor 9 (TLR9). Nucleic acid encoding CpG motifs or islands are plentiful in prokaryotes, and, thus, the CpG motif can be included in, or can be a part of, a bacterial gene that is encoded on the plasmid. For example, the bacterial gene asd contains immunostimulatory CpGs.

The immunostimulatory bacteria provided herein can be auxotrophic for adenosine, or adenosine and adenine. Any of the bacteria herein can be rendered auxotrophic for adenosine, which advantageously can increase the anti-tumor activity, since adenosine accumulates in many tumors, and is immunosuppressive.

The immunostimulatory bacteria provided herein can be flagellin deficient, where the wild-type bacterium comprises flagella. They can be rendered flagellin deficient by disrupting or deleting all or a part of the gene or genes that encode the flagella. For example, provided are immunostimulatory bacteria that have deletions in the genes encoding one or both of flagellin subunits fliC and fljB, whereby the bacteria is flagella deficient.

The immunostimulatory bacteria provided herein can include nucleic acid encoding cytoLLO, which is a listeriolysin O (LLO) protein lacking the periplasmic secretion signal sequence, so that it accumulates in the cytoplasm. This mutation is advantageously combined with asd⁻ bacteria. LLO is a cholesterol-dependent pore forming hemolysin from Listeria monocytogenes that mediates phagosomal escape of bacteria. When the autolytic strain is introduced into tumor-bearing hosts, such as humans, the bacteria are taken up by phagocytic immune cells and enter the vacuole. In this environment, the lack of DAP prevents bacterial replication, and results in autolysis of the bacteria in the vacuole. Lysis then releases the plasmid and the accumulated LLO forms pores in the cholesterol-containing vacuole membrane and allows for delivery of the plasmid into the cytosol of the host cell.

The immunostimulatory bacteria can include a DNA nuclear targeting sequence (DTS), such as an SV40 DTS, encoded on the plasmid.

The immunostimulatory bacteria can have a deletion or modification in the gene encoding endonuclease-1 (endA), whereby endA activity is inhibited or eliminated. Exemplary of these are immunostimulatory bacteria that contain one or more of a CpG motif, an asd gene selectable marker for plasmid maintenance and a DNA nuclear targeting sequence.

The immunostimulatory bacteria can contain nucleic acids on the plasmid encoding two or more different RNA molecules that inhibit, suppress or disrupt expression of an immune checkpoint or an RNA molecule that encodes an inhibitor of a metabolite that is immunosuppressive or is in an immunosuppressive pathway.

The nucleic acids encoding the RNAi, such as shRNA or miRNA or siRNA can include a transcriptional terminator following the RNA-encoding nucleic acid. In all embodiments, the RNAi encoded on the plasmid in the immunostimulatory bacteria can be short hairpin RNAs (shRNAs) or micro-RNAs (miRNAs).

The immunostimulatory bacteria can additionally encode a therapeutic product, such as RNAi that inhibits, suppresses, disrupts or silences expression of immune checkpoints and other targets whose inhibition, suppression, disruption or silencing is immunostimulatory, or an antibody or other binding protein that inhibits expression of these targets. These targets include, but are not limited to, one or more of three prime repair exonuclease 1 (TREX1), PD-1, PD-L1 (B7-H1), VEGF, TGF-beta isoform 1, beta-catenin, CTLA-4, PD-L2, PD-2, IDO1, IDO2, SIRPα, CD47, VISTA (B7-H5), LIGHT, HVEM, CD28, LAG3, TIM3, TIGIT, Galectin-9, CEACAM1, CD155, CD112, CD226, CD244 (2B4), B7-H2, B7-H3, ICOS, GITR, B7-H4, B7-H6, CD27, CD40, CD40L, CD48, CD70, CD80, CD86, CD137 (4-1BB), CD200, CD272 (BTLA), CD160, CD39, CD73, A2a receptor, A2b receptor, HHLA2, ILT-2, ILT-4, gp49B, PIR-B, HLA-G, ILT-2/4, OX40, OX-40L, KIR, TIM1, TIM4, STAT3, Stabilin-1 (CLEVER-1), DNase II and RNase H2. For example, any of the immunostimulatory bacteria can contain RNA that inhibits, suppresses or disrupts expression of one or a combination of TREX1, PD-L1, VISTA, TGF-beta, such as TGF-beta isoform 1 or isoforms 1 and 3, beta-catenin, SIRP-alpha, VEGF, RNase H2, DNase II, and CLEVER-1/Stabilin-1. Cluster of Differentiation 47 (CD47), also known as integrin associated protein (IAP), is a transmembrane receptor belonging to the immunoglobulin superfamily of proteins. CD47 is ubiquitously expressed on cells and serves as a marker for self-recognition, preventing phagocytosis. CD47 mediates its effects through interactions with several other proteins, including thrombospondin (TSP) and signal regulatory protein-alpha (SIRPα). The interaction between SIRPα on phagocytic cells and CD47 on target cells helps ensure that target cells do not become engulfed by the phagocytic cells. Certain cancers co-opt the CD47-based immune evasion mechanism of a cell by increasing expression of CD47 on the cell surface of the cancer cell, thus avoiding clearance by the immune system. Targeting CD47-expressing cells in a subject results in toxicities. Encoding a CD47 inhibitory molecule, such as an antibody or antibody fragment, such as a nanobody (see, e.g., Sockolosky et al. (2016) Proc. Natl. Acad. Sci. U.S.A. 113:E2646-E2654) on plasmids in the immunostimulatory bacteria provided herein results in expression of the anti-CD47 product in the tumor microenvironment or tumor. Anti-CD47 antibody fragments have been encoded in bacteria, such as E. coli that are administered intratumorally (see, e.g., Chowdhury et al. (2019) Nature Medicine 25:1057-1063). The bacteria herein have improved targeting and colonization of the tumor microenvironment, tumors, and/or tumor-resident immune cells, and, thus, can more effectively deliver the anti-CD47 antibody or antibody fragment. The immunostimulatory bacteria provided herein can be systemically administered to colonize tumors and the tumor microenvironment.

Provided are immunostimulatory bacteria where the plasmid comprises a sequence of nucleotides that encode a therapeutic product that inhibits an immune checkpoint or other immune suppressing target. Targets include, but are not limited to, TREX1, PD-L1, VISTA, TGF-beta isoform 1, beta-catenin, SIRP-alpha, VEGF, RNase H2, DNase II, CLEVER-1/Stabilin-1, and CD47. Other targets to be inhibited, suppressed or disrupted, are selected from among any of CTLA-4, PD-L2, PD-1, PD-2, IDO1, IDO2, LIGHT, HVEM, CD28, LAG3, TIM3, TIGIT, Galectin-9, CEACAM1, CD155, CD112, CD226, CD244 (2B4), B7-H2, B7-H3, ICOS, GITR, B7-H4, B7-H6, CD27, CD40, CD40L, CD48, CD70, CD80, CD86, CD137 (4-1BB), CD200, CD272 (BTLA), CD160, CD39, CD73, A2a receptor, A2b receptor, HHLA2, ILT-2, ILT-4, gp49B, PIR-B, HLA-G, ILT-2/4, OX40, OX-40L, KIR, TIM1, TIM4, and STAT3. Exemplary thereof are among human PD-L1 (SEQ ID NO:31), human beta-catenin (SEQ ID NO:32), human SIRPα (SEQ ID NO:33), human TREX1 (SEQ ID NO:34), human VISTA (SEQ ID NO:35), human TGF-beta isoform 1 (SEQ ID NO: 193), and human VEGF (SEQ ID NO: 194). RNA can target or contain a sequence in the immune checkpoint nucleic acids set forth in any of SEQ ID NOs: 1-30, 36-40, and 195-217. The plasmids in any of the immunostimulatory bacteria also can encode a sequence of nucleotides that is an agonist of retinoic acid-inducible gene I (RIG-I) or a RIG-I binding element.

The immunostimulatory bacteria can include one or more of deletions in genes, for example, the bacteria can be one or more of purI⁻ (purM⁻), msbB⁻, purD⁻, flagellin⁻ (fliC⁻/fljB⁻), pagP⁻, adrA⁻, csgD⁻ and hilA⁻. The immunostimulatory bacteria can be msbB⁻. For example, the immunostimulatory bacteria can contain a purI deletion, an msbB deletion, an asd deletion, an adrA deletion, and optionally, a csgD deletion. Exemplary of bacterial gene deletions/modifications are any of the following:

one or more of a mutation in a gene that alters the biosynthesis of lipopolysaccharide, selected from among one or more of rfaL, rfaG, rfaH, rfaD, rfaP, rFb, rfa, msbB, htrB, firA, pagL, pagP, lpxR, arnT, eptA, and lpxT; and/or

one or more of a mutation that introduces a suicide gene and is selected from one or more of sacB, nuk, hok, gef, kil or phlA; and/or

one or more of a mutation that introduces a bacterial lysis gene and is selected from one or both of hly and cly; and/or

a mutation in one or more virulence factor(s), selected from among IsyA, pag, prg, iscA, virG, plc and act; and/or

one or more of a mutation in a gene that modifies the stress response, selected from among recA, htrA, htpR, hsp and groEL; and/or

a mutation in min that disrupts the cell cycle; and/or

one or more mutations in genes that disrupt or inactivate regulatory functions, selected from among cya, crp, phoP/phoQ, and ompR.

The immunostimulatory bacterium can be a strain of Salmonella, Shigella, E. coli, Bifidobacteriae, Rickettsia, Vibrio, Listeria, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Cholera, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Bacillus, or Erysipelothrix, or an attenuated strain thereof or modified strain thereof of any of the preceding list of bacterial strains.

Exemplary of the immunostimulatory bacteria are those where the plasmid contains one or more of a sequence of nucleic acids encoding a listeriolysin O (LLO) protein lacking the signal sequence (cytoLLO), a CpG motif, a DNA nuclear targeting sequence (DTS), and a retinoic acid-inducible gene-I (RIG-I) binding element.

Other exemplary immunostimulatory bacteria include those that are auxotrophic for adenosine, and comprise: a deletion in the gene(s) encoding the flagella; a deletion in endA; a plasmid that encodes CytoLLO; a nuclear localization sequence; and an asd plasmid complementation system; and encode RNA that inhibits, suppresses or disrupts expression of an immune checkpoint or other target whose inhibition, suppression or disruption increases the anti-tumor immune response in a subject.

Such immunostimulatory bacteria include strains of Salmonella, such as a wild type Salmonella typhimurium strain, such as the strain deposited under ATCC accession no. 14028, or a strain having all of the identifying characteristics of the strain deposited under ATCC accession #14028. Other strains include, for example, an attenuated Salmonella typhimurium strain selected from among strains designated as AST-100, VNP20009, or strains YS1646 (ATCC #202165), RE88, SL7207, χ8429, χ8431, and χ8468.

The immunostimulatory bacteria can contain one or more of a purI⁻ deletion, an msbB deletion, an asd deletion, and an adrA deletion, in addition to the modifications that increase accumulation in tumor cells, the TME, and/or tumor-resident immune cells, and/or modifications that reduce immune cell death, and can encode an immunostimulatory protein or other therapeutic product as described herein. The immunostimulatory bacteria also can include:

one or more of a mutation in a gene that alters the biosynthesis of lipopolysaccharide selected from among one or more of rfaL, rfaG, rfaH, rfaD, rfaP, rFb, rfa, msbB, htrB, firA, pagL, pagP, lpxR, arnT, eptA, and lpxT; and/or

one or more of a mutation that introduces a suicide gene and is selected from among one or more of sacB, nuk, hok, gef, kil and phlA; and/or

one or more of a mutation that introduces a bacterial lysis gene and is selected from among one or both of hly and cly; and/or

a mutation in one or more virulence factor(s) selected from among IsyA, pag, prg, iscA, virG, plc and act; and/or

one or more mutations in a gene or genes that modify the stress response selected from among recA, htrA, htpR, hsp and groEL; and/or

a mutation in min that disrupts the cell cycle; and/or

one or more mutations that disrupt or inactivate regulatory functions selected from among cya, crp, phoP/phoQ and ompR.

The strains can be one or more of msbB⁻, asd⁻, hilA⁻ and/or flagellin⁻ (fliC⁻/fljB⁻), and/or pagP⁻. In particular, the strains are flagellin⁻ (fliC⁻/fljB⁻), such as flagellin⁻ (fliC⁻/fljB⁻), msbB⁻, purI⁻/M⁻, and optionally asd⁻ and/or HilA⁻. The bacteria can be auxotrophic for adenosine, or adenosine and adenine. The therapeutic product, such as RNAi and/or an immunostimulatory protein, and/or antibody or fragment thereof, are expressed under control of a promoter recognized by the host, such as an RNAP III promoter or an RNAP II promoter, as described herein. The immunostimulatory bacterium can be a strain of Salmonella, Shigella, E. coli, Bifidobacteriae, Rickettsia, Vibrio, Listeria, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Cholera, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Bacillus, or Erysipelothrix, or an attenuated strain thereof or modified strain thereof of any of the preceding list of bacterial strains. Generally, the strain is one that is attenuated in the host. Salmonella strains, such as S. typhimurium, are exemplary of the bacteria. Exemplary strains include Salmonella typhimurium strains derived from strains designated as AST100, VNP20009, or strains YS1646 (ATCC #202165), RE88, SL7207, χ8429, χ8431, χ8468, and the wild-type strain ATCC #14028.

Compositions containing the immunostimulatory bacteria are provided. Such compositions contain the bacteria and a pharmaceutically acceptable excipient or vehicle. The immunostimulatory bacteria include any described herein or in patents/applications incorporated herein or known to those of skill in the art. The bacteria encode a therapeutic product, generally an anti-cancer product such as an inhibitor of an immune checkpoint or an immunostimulatory protein that increases anti-tumor activity in the tumor microenvironment or in the tumor, such as a cytokine or chemokine or co-stimulatory molecule. The genomes of the bacteria can be modified to have increased infectivity of immune cells, and or reduced infectivity of non-immune cells, and/or reduced ability to induce cell death of immune cells. Hence, the bacteria are modified as described herein to accumulate in tumors or the tumor microenvironment or tumor-resident immune cells, and/or to deliver immunostimulatory proteins and other therapeutic products that promote anti-tumor activity. The immunostimulatory bacteria can additionally contain a plasmid encoding a therapeutic anti-cancer product, such as RNAi, such as miRNA or shRNA, or a CRISPR cassette, that target an immune checkpoint, or otherwise enhance the anti-tumor activity of the bacteria.

A single dose is therapeutically effective for treating a disease or disorder in which immune stimulation effects treatment. Exemplary of such stimulation is an immune response, that includes, but is not limited to, one or both of a specific immune response and non-specific immune response, both specific and non-specific immune responses, an innate response, a primary immune response, adaptive immunity, a secondary immune response, a memory immune response, immune cell activation, immune cell proliferation, immune cell differentiation, and cytokine expression.

Pharmaceutical compositions containing any of the immunostimulatory bacteria are provided. As are uses thereof for treatment of cancers, and methods of treatment of cancer. Methods and uses include treating a subject who has cancer, comprising administering an immunostimulatory bacterium or the pharmaceutical composition to a subject, such as a human. A method of treating a subject who has cancer, comprising administering an immunostimulatory bacterium, is provided.

Methods and uses include combination therapy in which a second anti-cancer agent or treatment is administered. The second anti-cancer agent is a chemotherapeutic agent that results in cytosolic DNA, or radiotherapy, or an anti-immune checkpoint inhibitor, such as an anti-PD-1, or anti-PD-L1 or anti-CTLA4 antibody, or CAR-T cells or other therapeutic cells, such as stem cells, TIL cells and modified cells for cancer therapy. The combination therapy also can include anti-VEGF or anti-VEGFR, or anti-VEGFR2 antibodies, or fragments thereof, or an anti-IL6 antibody or fragment thereof, or oncolytic virus therapy, or a cancer vaccine.

Administration can be by any suitable route, such as parenteral, and can include additional agents that can facilitate or enhance delivery. Administration can be oral or rectal or by aerosol into the lung, or can be intratumorally, intravenously, intramuscularly, or subcutaneously.

Cancers include solid tumors and hematologic malignancies, such as, but not limited to, lymphoma, leukemia, gastric cancer, and cancer of the breast, heart, lung, small intestine, colon, spleen, kidney, bladder, head and neck, colorectum, ovary, prostate, brain, pancreas, skin, bone, bone marrow, blood, thymus, uterus, testicles, cervix, and liver.

The immunostimulatory bacteria can be formulated into compositions for administration, such as suspensions. They can be dried and stored as powders. Combinations of the immunostimulatory bacteria with other anti-cancer agents also are provided.

Combination therapies for treatment of cancers and malignancies are provided. The immunostimulatory bacteria can be administered before, or concurrently with, other cancer therapies, including radiotherapy, chemotherapies, particularly genotoxic chemotherapies that result in cytosolic DNA, and immunotherapies, such as anti-checkpoint inhibitor antibodies, including anti-PD-1 antibodies, anti-PD-L1 antibodies, and anti-CTLA4 antibodies, and other such immunotherapies. Other cancer therapies also include anti-VEGF, anti-VEGFR, anti-VEGFR2, or anti-IL6 antibodies, or fragments thereof, cancer vaccines and oncolytic viruses.

Administration can be by any suitable route, including systemic or local or topical, such as parenteral, including, for example, oral or rectal or by aerosol into the lung, or intratumorally, intravenously, intramuscularly, or subcutaneously.

Also provided are methods for increasing the colonization of tumors, tumor-resident immune cells, and/or the tumor microenvironment by an immunostimulatory bacterium. The methods include, for example, modifying the genome of a bacterium to render the bacterium flagellin⁻ (fliC⁻/fljB⁻) and/or pagP⁻. It is shown herein that such modification(s) strikingly enhance tumor/tumor microenvironment/tumor-resident immune cell colonization.

The terms and expressions that are employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic of the process used to delete the asd gene from strain YS1646. The asd gene from S. typhimurium strain YS1646 was deleted using lambda-derived Red recombination system as described in Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645 (2000)).

FIG. 2 depicts the levels of tumor colonization in injected and distal tumors after IT administration of AST-104. BALB/c mice (6-8 week old) were implanted with dual CT26 (2×10⁵ cells) subcutaneous flank tumors on the right and left flanks (n=10 per group). Mice with established tumors were IT injected into the right flank with 5×10⁶ CFU of the YS1646 strain containing a TREX1 shRNA plasmid (AST-104). At 35 days post tumor implantation (12 days after the last dose of AST-104), three mice were sacrificed, and injected and distal tumors were homogenized (GentleMACs™, Miltenyi Biotec) and plated on LB plates to enumerate the number of colony forming units (CFU) per gram of tumor tissue. The figure depicts the mean CFU per gram of tissue, +SD.

FIG. 3 depicts that CpG scrambled plasmid has immuno-stimulatory anti-tumor properties. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the YS1646 strain (AST-100), or the YS1646 strain containing the scrambled shRNA control plasmid (AST-103), or PBS control, on the days indicated by the arrows. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width²). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations. TGI is calculated as 1-(mean test tumor volume/mean control tumor volume)×100. The figure depicts mean tumor growth of each group, ±SEM. **p<0.01, student's t-test.

FIG. 4 depicts a schematic of the process used to delete the fliC gene. The flic gene was deleted from the chromosome of S. typhimurium strain AST-101 (asd deleted strain of YS1646) using lambda-derived Red recombination system as described in Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645 (2000)).

FIG. 5 depicts that the flagellin deletion strain grows normally in LB. The figure depicts the growth of strains AST-108 ASD (pATI-shTREX1) and AST-112 ASD/FLG (pATI-shTREX1) at 37° C. in LB broth, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices).

FIG. 6 depicts that flagellin knockout improves anti-tumor efficacy. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd/fljB/fliC knockout strain containing the pATI shTREX1 plasmid (AST-113), or asd knockout strain containing the pATI shTREX1 plasmid (AST-110), or PBS control, on the days indicated by the arrows. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width²). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations. TGI was calculated as 1-(mean test tumor volume/mean control tumor volume)×100. The figure depicts the mean tumor growth of each group, ±SEM. *p<0.05, student's t-test.

FIG. 7 depicts that flagellin knockout shows an increased IFN-gamma signature. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd/fljB/fliC knockout strain containing the pATI shTREX1 plasmid (AST-113), or asd knockout strain containing the pATI shTREX1 plasmid (AST-110), or PBS control. Mice were bled 6 hours following the first dose and systemic serum cytokines tested by Luminex 200 device (Luminex Corporation) and mouse cytometric bead array (BD bead array, FACS Fortessa, FCAP software, all BD Biosciences). *p<0.05, **p<0.01, ***p<0.001, student's t-test.

FIG. 8 depicts that flagellin is not required for tumor colonization. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd/fljB/fliC knockout strain containing the pATI shTREX1 plasmid (AST-113), or asd knockout strain containing the pATI shTREX1 plasmid (AST-110), or PBS control. At 35 days (D35) post tumor implantation (12 days after the last dose of engineered Salmonella therapy), three mice per group were sacrificed, and tumors were homogenized (GentleMACs™, Miltenyi Biotec) and plated on LB plates to enumerate the number of colony forming units per gram of tumor tissue. The figure depicts the mean colony forming units (CFU) per gram of tissue, ±SD.

FIG. 9 depicts that a cytoLLO expressing strain grows normally in vitro. The figure depicts the growth of strains AST-110 (YS1646 with asd deletion containing (pATI-shTREX1)) and AST-115 (YS1646 with asd deletion and knock-in of cytoLLO expression cassette containing (pATI-shTREX1)) at 37° C. in LB broth, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices).

FIG. 10 depicts that AST-115 (ASD knockout+CytoLLO Knock-in strain carrying shTREX1 plasmid) demonstrates potent, single-dose efficacy in a murine CT26 tumor model. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of AST-115 (YS1646 with asd deletion and knock-in of cytoLLO expression cassette at asd locus containing (pATI-shTREX1)), or PBS control, on the days indicated by the arrows. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width²). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations. TGI was calculated as 1-(mean test tumor volume/mean control tumor volume)×100. The figure depicts the mean tumor growth of each group, ±SEM. **p<0.01, student's t-test.

FIG. 11 depicts that strain YS1646 requires tumor microenvironment levels of adenosine for growth. Growth of strains YS1646 (purI⁻/msbB⁻) and the wild-type parental strain ATCC14028 at 37° C. in LB broth are shown, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices).

FIG. 12 depicts that ASD, FLG, and CytoLLO engineered strains require high adenosine for growth. The growth of strains AST-117 (YS1646 Δasd containing a low copy shTREX-1 plasmid), AST-118 (YS1646 Δasd/ΔfliC/ΔfljB containing a low copy shTREX-1 plasmid), and AST-119 (YS1646 Δasd:LLO containing a low copy shTREX-1 plasmid) at 37° C. in LB broth are shown, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices).

FIG. 13 depicts that a strain with a low copy origin of replication asd-encoding plasmid has superior growth kinetics than a strain with a high copy origin of replication asd-encoding plasmid. The growth of strains YS1646, AST-117 (YS1646 Δasd containing a low copy shTREX-1 plasmid with a functional asd gene), AST-104 (YS1646 containing a low copy pEQ shTREX-1 plasmid without an asd gene), and AST-110 (YS1646 Δasd containing a high copy pATI-shTREX-1 plasmid with a functional asd gene) at 37° C. in LB broth are shown, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices).

FIG. 14 depicts that a strain with a low copy asd plasmid is more fit than a strain with a high copy asd plasmid in mouse tumor cells. The intracellular growth of strains AST-117 (YS1646 Δasd containing a low copy shTREX-1 plasmid with a functional asd gene) and AST-110 (YS1646 Δasd containing a high copy pATI-shTREX-1 plasmid with a functional asd gene) are shown in B16F. 10 mouse melanoma cells and CT26 mouse colon carcinoma cells. 5×10⁵ cells in a 24 well dish were infected with the S. typhimurium strains at a MOI of 5. After 30 minutes of infection, media was replaced with media containing gentamycin to kill extracellular bacteria. At indicated time points, cell monolayers were lysed by osmotic shock the cell lysates were diluted and plated on LB agar to enumerate CFU.

FIG. 15 depicts that in vivo, asd gene complementation systems result in retention of plasmids in S. typhimurium-infected tumors. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd knockout strain containing the pATI shTREX1 plasmid (AST-110) or the YS1646 containing a pEQ shTREX-1 plasmid without an asd gene (AST-104). At 35 days post tumor implantation (12 days after the last dose of engineered Salmonella therapy), three mice per group were sacrificed, and tumors were homogenized using a GentleMACs™ homogenizer (Miltenyi Biotec) and plated on LB agar plates or LB agar plates with 50 ug/mL of Kanamycin. The figure depicts the percentage of Kanamycin resistant CFU in tumor tissue homogenates, ±SD.

FIG. 16 depicts that the therapeutic efficacy of a strain containing a plasmid with asd gene complementation system and shTREX1 (AST-110) is improved. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd knockout strain containing the pATI-shTREX1 plasmid (AST-110) or the asd knockout strain containing the pATI-scramble plasmid (AST-109), or the YS1646 strain containing a pEQ-shTREX-1 plasmid without an asd gene (AST-104), or PBS control, on the days indicated by the arrows. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width²). Mice were euthanized when tumor size reaches >20% of body weight or became necrotic, as per IACUC regulations. TGI was calculated as 1−(mean test tumor volume/mean control tumor volume)×100. The figure depicts the mean tumor growth of each group, ±SEM.

FIG. 17 depicts that a strain containing a low copy shTREX1 plasmid (AST-117) has superior anti-tumor properties compared to a strain containing a high copy plasmid (AST-110). BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd knockout strain containing the pATI-shTREX1 plasmid with a high copy number origin of replication (AST-110) or the asd knockout strain containing the pATI-shTREX1 plasmid with a low copy number origin of replication (AST-117), or PBS control, on the days indicated by the arrows. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width²). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations. TGI was calculated as 1-(mean test tumor volume/mean control tumor volume)×100. The figure depicts the mean tumor growth of each group, ±SEM. *p<0.05, student's t-test.

FIGS. 18A and 18B depict that the AST-117 low copy plasmid strain colonizes tumors better and has a higher tumor to spleen colonization ratio than the AST-110 high copy plasmid strain. BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the asd knockout strain containing the pATI-shTREX1 plasmid with a high copy number origin of replication (AST-110) or the asd knockout strain containing the pATI-shTREX1 plasmid with a low copy number origin of replication (AST-117). At 35 days post tumor implantation (12 days after the last dose of engineered Salmonella therapy), 3 mice per group were sacrificed, and tumors were homogenized using a GentleMACs™ homogenizer (Miltenyi Biotec) and plated on LB plates to enumerate the number of CFU per gram of tumor tissue. FIG. 18A depicts the mean CFU per gram of tumor tissue, +SD. FIG. 18B depicts the tumor to spleen colonization ratios.

FIG. 19 depicts that autolytic strain (AST-120) cannot grow in the absence of DAP. The figure depicts the growth of Δasd:cytoLLO strain containing a pEQU6-shTREX1 plasmid that does not contain an asd gene (AST-120) over time in LB broth alone, or in LB broth supplemented with 50 μg/mL DAP, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices).

FIG. 20 depicts the anti-tumor activity of the autolytic strain (AST-120). BALB/c mice (6-8 week old) were implanted with a single CT26 (2×10⁵ cells) subcutaneous flank tumor (n=9 per group). Mice with established tumors were IV injected with 5×10⁶ CFU of the of Δasd:cytoLLO strain containing a pEQU6-shTREX1 plasmid that does not contain an asd gene (AST-120), or PBS control, on the days indicated by the arrows. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width²). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations. TGI was calculated as 1-(mean test tumor volume/mean control tumor volume)×100. The figure depicts the mean tumor growth of each group, ±SEM. *p<0.05, student's t-test.

FIG. 21 depicts proteins that act downstream of HilA in the SPI-1 pathway.

FIG. 22 depicts the SPI-1 T3SS and the functional classification of SPI-1 encoded proteins (adapted from Kimbrough and Miller (2002) Microbes Infect. 4(1):75-82).

FIG. 23 depicts the effects of the SPI-1 T3SS on macrophages. Flagellin is detected by NAIP5/6 and the rod and needle proteins are detected by NAIP1/2, which leads to activation of the NLRC4 inflammasome and caspase-1, resulting in the release of IL-1β and IL-18, and pyroptosis.

FIG. 24 depicts T3SS-1-mediated entry of the bacterium into the epithelial cell and the SCV.

FIG. 25 depicts recognition of bacterial flagellin by TLR5 and LPS by TLR4, and the role that flagellin, LPS, HilA, PrgI and PrgJ play in host cell infection, cytokine release, inflammasome activation, and pyroptosis.

DETAILED DESCRIPTION

OUTLINE

-   -   A. DEFINITIONS     -   B. OVERVIEW OF THE IMMUNOSTIMULATORY BACTERIA     -   C. CANCER IMMUNOTHERAPEUTICS         -   1. Immunotherapies         -   2. Adoptive Immunotherapies         -   3. Cancer Vaccines and Oncolytic Viruses     -   D. BACTERIAL CANCER IMMUNOTHERAPY         -   1. Bacterial Therapies         -   2. Comparison of the Immune Responses to Bacteria and             Viruses         -   3. Salmonella Therapy             -   a. Tumor-tropic Bacteria.             -   b. Salmonella enterica Serovar Typhimurium             -   c. Bacterial Attenuation                 -   i. msbB Mutants                 -   ii. purI⁻ Mutants                 -   iii. Combinations of Attenuating Mutations                 -   iv. VNP20009 and Other Attenuated and Wild-type S.                     typhimurium Strains                 -   v. S. typhimurium Engineered To Deliver                     Macromolecules         -   4. Enhancements of Immunostimulatory Bacteria to Increase             Therapeutic Index             -   a. asd Gene Deletion             -   b. Adenosine Auxotrophy             -   c. Flagellin Deficient Strains             -   d. Salmonella Engineered to Escape the Salmonella                 Containing Vacuole (SCV)             -   e. Deletions in Salmonella Genes Required for Biofilm                 Formation             -   f. Deletions in Genes in the LPS Biosynthetic Pathway             -   g. Deletions of SPI-1 and SPI-2 Genes             -   h. Endonuclease (endA) Mutations To Increase Plasmid                 Delivery             -   i. RIG-I Inhibition             -   j. DNase II Inhibition             -   k. RNase H2 Inhibition             -   l. Stabilin-1/CLEVER-1 Inhibition         -   5. Immunostimulatory Proteins         -   6. Modifications that Increase Uptake of Gram-negative             Bacteria, such as Salmonella, by Immune Cells and Reduce             Immune Cell Death         -   7. Bacterial Culture Conditions     -   E. BACTERIAL ATTENUATION AND COLONIZATION         -   1. Deletion of flagellin (fliC/fljB)         -   2. Deletion of Genes in the LPS Biosynthetic Pathway         -   3. Colonization     -   F. CONSTRUCTING EXEMPLARY PLASMIDS ENCODING THERAPEUTIC PROTEINS         -   1. Immunostimulatory Proteins         -   2. Antibodies and Antibody Fragments         -   3. Interfering RNAs (RNAi)             -   a. shRNA             -   b. MicroRNA         -   4. Origin of Replication and Plasmid Copy Number         -   5. CpG Motifs and CpG Islands         -   6. Plasmid Maintenance/Selection Components         -   7. RNA Polymerase Promoters         -   8. DNA Nuclear Targeting Sequences         -   9. CRISPR     -   G. TUMOR-TARGETING IMMUNOSTIMULATORY BACTERIA CONTAIN RNAI         AGAINST EXEMPLARY IMMUNE TARGET GENES TO STIMULATE ANTI-TUMOR         IMMUNITY         -   1. TREX1         -   2. PD-L1         -   3. VISTA         -   4. SIRPα         -   5. β-catenin         -   6. TGF-β         -   7. VEGF         -   8. Additional Exemplary Checkpoint Targets     -   H. PHARMACEUTICAL PRODUCTION, COMPOSITIONS, AND FORMULATIONS         -   1. Manufacturing             -   a. Cell Bank Manufacturing             -   b. Drug Substance Manufacturing             -   c. Drug Product Manufacturing         -   2. Compositions         -   3. Formulations             -   a. Liquids, Injectables, Emulsions             -   b. Dried Thermostable Formulations         -   4. Compositions for Other Routes of Administration         -   5. Dosages and Administration         -   6. Packaging and Articles of Manufacture     -   I. METHODS OF TREATMENT AND USES         -   1. Tumors         -   2. Administration         -   3. Monitoring     -   J. EXAMPLES

A. DEFINITIONS

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which the invention(s) belong. All patents, patent applications, published applications and publications, GenBank sequences, databases, websites and other published materials referred to throughout the entire disclosure herein, unless noted otherwise, are incorporated by reference in their entirety. In the event that there are a plurality of definitions for terms herein, those in this section prevail. Where reference is made to a URL or other such identifier or address, it is understood that such identifiers can change and particular information on the internet can come and go, but equivalent information can be found by searching the internet. Reference thereto evidences the availability and public dissemination of such information.

As used herein, therapeutic bacteria are bacteria that effect therapy, such as cancer or anti-tumor therapy, when administered to a subject, such as a human.

As used herein, immunostimulatory bacteria are therapeutic bacteria that, when introduced into a subject, accumulate in immunoprivilaged tissues and cells, such as tumors, and replicate and/or express products that are immunostimulatory or that result in immunostimulation. For example, the immunostimulatory bacteria are attenuated in the host by virtue of reduced toxicity or pathogenicity and/or by virtue of encoded products that reduce toxicity or pathogenicity, as the immunostimulatory bacteria cannot replicate and/or express products (or have reduced replication/product expression), except primarily in immunoprivilaged environments. Immunostimulatory bacteria provided herein are modified to encode a product or products or exhibit a trait or property that renders them immunostimulatory. Such products, properties and traits include, but are not limited to, for example, at least one of: an immunostimulatory protein, such as a cytokine, chemokine or co-stimulatory molecule; RNAi, such as siRNA (shRNA and microRNA), or CRISPR, that targets, disrupts or inhibits an immune checkpoint gene such as TREX1 and/or PD-L1; or an inhibitor of an immune checkpoint such as an anti-immune checkpoint antibody. Immunostimulatory bacteria also can include a modification that renders the bacterium auxotrophic for a metabolite that is immunosuppressive or that is in an immunosuppressive pathway, such as adenosine.

As used herein, the strain designations VNP20009 (see, e.g., International PCT Application Publication No. WO 99/13053, see, also U.S. Pat. No. 6,863,894) and YS1646 and 41.2.9 are used interchangeably and each refer to the strain deposited with the American Type Culture Collection (ATCC) and assigned Accession No. 202165. VNP20009 is a modified attenuated strain of Salmonella typhimurium, which contains deletions in msbB and purI, and was generated from wild type strain ATCC #14028.

As used herein, the strain designations YS1456 and 8.7 are used interchangeably and each refer to the strain deposited with the American Type Culture Collection and assigned Accession No. 202164 (see, U.S. Pat. No. 6,863,894).

As used herein, an origin of replication is a sequence of DNA at which replication is initiated on a chromosome, plasmid or virus. For small DNA, including bacterial plasmids and small viruses, a single origin is sufficient.

The origin of replication determines the vector copy number, which depends upon the selected origin of replication. For example, if the expression vector is derived from the low-copy-number plasmid pBR322, it is between about 25-50 copies/cell, and if derived from the high-copy-number plasmid pUC, it can be 150-200 copies/cell.

As used herein, medium copy number of a plasmid in cells is about or is 150 or less than 150, low copy number is 15-30, such as 20 or less than 20. Low to medium copy number is less than 150. High copy number is greater than 150 copies/cell.

As used herein, a CpG motif is a pattern of bases that include an unmethylated central CpG (“p” refers to the phosphodiester link between consecutive C and G nucleotides) surrounded by at least one base flanking (on the 3′ and the 5′ side of) the central CpG. A CpG oligodeoxynucleotide is an oligodeoxynucleotide that is at least about ten nucleotides in length and includes an unmethylated CpG. At least the C of the 5′ CG 3′ is unmethylated.

As used herein, a RIG-I binding sequence refers to a 5′triphosphate (5′ppp) structure directly, or that which is synthesized by RNA pol III from a poly(dA-dT) sequence, which by virtue of interaction with RIG-I can activate type I IFN via the RIG-I pathway. The RNA includes at least four A ribonucleotides (A-A-A-A); it can contain 4, 5, 6, 7, 8, 9, 10 or more. The RIG-I binding sequence is introduced into a plasmid in the bacterium for transcription into the polyA.

As used herein, an immunostimulatory protein is one that confers, promotes, enhance or increases immune responses, particularly in the tumor microenvironment, such as in tumors and/or in tumor-resident immune cells. Immunostimulatory proteins include, but are not limited to, cytokines, chemokines, co-stimulatory molecules, and other immune regulatory proteins and products. Thus, as used herein, an “immunostimulatory protein” is a protein that confers, exhibits or promotes an anti-tumor immune response in the tumor microenvironment. Exemplary of such proteins are cytokines, chemokines, and co-stimulatory molecules, such as, but not limited to, GM-CSF, IL-2, IL-7, IL-12, IL-15, IL-18, IL-21, IL-12p70 (IL-12p40+IL-12p35), IL-15/IL-15R alpha chain complex, CXCL9, CXCL10, CXCL11, CCL3, CCL4, CCL5, molecules involved in the potential recruitment/persistence of T cells, CD40, CD40 ligand (CD40L), OX40, OX40 ligand (OX40L), 4-1BB, 4-1BB ligand (4-1BBL), members of the B7-CD28 family, CD47 antagonists, TGF-beta polypeptide antagonists, and members of the TNFR superfamily.

As used herein, “cytokines” are a broad and loose category of small proteins (˜5-20 kDa) that are important in cell signaling. Cytokines include chemokines, interferons, interleukins, lymphokines, and tumor necrosis factors. Cytokines are cell signaling molecules that aid cell to cell communication in immune responses, and stimulate the movement of cells towards sites of inflammation, infection and trauma.

As used herein, “chemokines” refer to chemoattractant (chemotactic) cytokines that bind to chemokine receptors and include proteins isolated from natural sources as well as those made synthetically, as by recombinant means or by chemical synthesis. Exemplary chemokines include, but are not limited to, IL-8, IL-10, GCP-2, GRO-α, GRO-β, GRO-γ, ENA-78, PBP, CTAP III, NAP-2, LAPF-4, MIG (CXCL9), CXCL10, CXCL11, PF4, IP-10, SDF-1α, SDF-1β, SDF-2, MCP-1, MCP-2, MCP-3, MCP-4, MCP-5, MIP-1α (CCL3), MIP-1β (CCL4), MIP-1γ, MIP-2, MIP-2α, MIP-3α, MIP-3β, MIP-4, MIP-5, MDC, HCC-1, ALP, lungkine, Tim-1, eotaxin-1, eotaxin-2, I-309, SCYA17, TRAC, RANTES (CCL5), DC-CK-1, lymphotactin, ALP, lungkine and fractalkine, and others known to those of skill in the art. Chemokines are involved in the migration of immune cells to sites of inflammation, as well as in the maturation of immune cells and in the generation of adaptive immune responses.

As used herein, a bacterium that is modified so that it “induces less cell death in tumor-resident immune cells” or “induces less cell death in immune cells” is one that is less toxic than the bacterium without the modification, or one that has reduced virulence compared to the bacterium without the modification. Exemplary of such modifications are those that decrease/eliminate pyroptosis and that alter lipopolysaccharide (LPS) profiles on the bacterium. These modifications include one or more of disruption of or deletion of flagellin genes, pagP, or one or more components of the SPI-1 pathway, such as hilA, rod protein, needle protein, and QseC.

As used herein, a bacterium that is “modified so that it preferentially infects tumor-resident immune cells” or “modified so that it preferentially infects immune cells” has a modification in its genome that reduces its ability to infect cells other than immune cells. Exemplary of such modifications are modifications that disrupt the type 3 secretion system or type 4 secretion system or other genes or systems that affect the ability of a bacterium to invade a non-immune cell. For example, disruption/deletion of an SPI-1 component, which is needed for infection of cells, such as epithelial cells, but does not affect infection of immune cells, such as phagocytic cells, by Salmonella.

As used herein, a “modification” is in reference to modification of a sequence of amino acids of a polypeptide or a sequence of nucleotides in a nucleic acid molecule and includes deletions, insertions, and replacements of amino acids or nucleotides, respectively. Methods of modifying a polypeptide are routine to those of skill in the art, such as by using recombinant DNA methodologies.

As used herein, a modification to a bacterial genome or to a plasmid or gene includes deletions, replacements and insertions of nucleic acid.

As used herein, RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules to inhibit translation and thereby expression of a targeted gene.

As used herein, RNA molecules that act via RNAi are referred to as inhibitory by virtue of their silencing of expression of a targeted gene. Silencing expression means that expression of the targeted gene is reduced or suppressed or inhibited.

As used herein, gene silencing via RNAi is said to inhibit, suppress, disrupt or silence expression of a targeted gene. A targeted gene contains sequences of nucleotides that correspond to the sequences in the inhibitory RNA, whereby the inhibitory RNA silences expression of mRNA.

As used herein, inhibiting, suppressing, disrupting or silencing a targeted gene refers to processes that alter expression, such as translation, of the targeted gene, whereby activity or expression of the product encoded by the targeted gene is reduced. Reduction, includes a complete knock-out or a partial knockout, whereby with reference to the immunostimulatory bacterium provided herein and administration herein, treatment is effected.

As used herein, small interfering RNAs (siRNAs) are small pieces of double-stranded (ds) RNA, usually about 21 nucleotides long, with 3′ overhangs (2 nucleotides) at each end that can be used to “interfere” with the translation of proteins by binding to and promoting the degradation of messenger RNA (mRNA) at specific sequences. In doing so, siRNAs prevent the production of specific proteins based on the nucleotide sequences of their corresponding mRNAs. The process is called RNA interference (RNAi), and also is referred to as siRNA silencing or siRNA knockdown.

As used herein, a short-hairpin RNA or small-hairpin RNA (shRNA) is an artificial RNA molecule with a tight hairpin turn that can be used to silence target gene expression via RNA interference (RNAi). Expression of shRNA in cells is typically accomplished by delivery of plasmids or through viral or bacterial vectors.

As used herein, a tumor microenvironment (TME) is the cellular environment in which the tumor exists, including surrounding blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, lymphocytes, signaling molecules and the extracellular matrix (ECM). Conditions that exist include, but are not limited to, increased vascularization, hypoxia, low pH, increased lactate concentration, increased pyruvate concentration, increased interstitial fluid pressure and altered metabolites or metabolism, such as higher levels of adenosine, indicative of a tumor.

As used herein, human type I interferons (IFNs) are a subgroup of interferon proteins that regulate the activity of the immune system. All type I IFNs bind to a specific cell surface receptor complex, such as the IFN-α receptor. Type I interferons include IFN-α and IFN-β, among others. IFN-β proteins are produced by fibroblasts, and have antiviral activity that is involved mainly in innate immune response. Two types of IFN-β are IFN-β1 (IFNB1) and IFN-β3 (IFNB3).

As used herein, recitation that a nucleic acid or encoded RNA targets a gene means that it inhibits or suppresses or silences expression of the gene by any mechanism. Generally, such nucleic acid includes at least a portion complementary to the targeted gene, where the portion is sufficient to form a hybrid with the complementary portion.

As used herein, “deletion,” when referring to a nucleic acid or polypeptide sequence, refers to the deletion of one or more nucleotides or amino acids compared to a sequence, such as a target polynucleotide or polypeptide or a native or wild-type sequence.

As used herein, “insertion,” when referring to a nucleic acid or amino acid sequence, describes the inclusion of one or more additional nucleotides or amino acids, within a target, native, wild-type or other related sequence. Thus, a nucleic acid molecule that contains one or more insertions compared to a wild-type sequence, contains one or more additional nucleotides within the linear length of the sequence.

As used herein, “additions” to nucleic acid and amino acid sequences describe addition of nucleotides or amino acids onto either termini compared to another sequence.

As used herein, “substitution” or “replacement” refers to the replacing of one or more nucleotides or amino acids in a native, target, wild-type or other nucleic acid or polypeptide sequence with an alternative nucleotide or amino acid, without changing the length (as described in numbers of residues) of the molecule. Thus, one or more substitutions in a molecule does not change the number of amino acid residues or nucleotides of the molecule. Amino acid replacements compared to a particular polypeptide can be expressed in terms of the number of the amino acid residue along the length of the polypeptide sequence.

As used herein, “at a position corresponding to,” or recitation that nucleotides or amino acid positions “correspond to” nucleotides or amino acid positions in a disclosed sequence, such as set forth in the Sequence Listing, refers to nucleotides or amino acid positions identified upon alignment with the disclosed sequence to maximize identity using a standard alignment algorithm, such as the GAP algorithm. By aligning the sequences, one skilled in the art can identify corresponding residues, for example, using conserved and identical amino acid residues as guides. In general, to identify corresponding positions, the sequences of amino acids are aligned so that the highest order match is obtained (see, e.g., Computational Molecular Biology, Lesk, A. M., ed., Oxford University Press, New York, 1988; Biocomputing: Informatics and Genome Projects, Smith, D. W., ed., Academic Press, New York, 1993; Computer Analysis of Sequence Data, Part I, Griffin, A. M., and Griffin, H. G., eds., Humana Press, New Jersey, 1994; Sequence Analysis in Molecular Biology, von Heinje, G., Academic Press, 1987; Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M Stockton Press, New York, 1991; and Carrillo et al. (1988) SIAM J Applied Math 48:1073).

As used herein, alignment of a sequence refers to the use of homology to align two or more sequences of nucleotides or amino acids. Typically, two or more sequences that are related by 50% or more identity are aligned. An aligned set of sequences refers to 2 or more sequences that are aligned at corresponding positions and can include aligning sequences derived from RNAs, such as ESTs and other cDNAs, aligned with genomic DNA sequence. Related or variant polypeptides or nucleic acid molecules can be aligned by any method known to those of skill in the art. Such methods typically maximize matches, and include methods, such as using manual alignments and by using the numerous alignment programs available (e.g., BLASTP) and others known to those of skill in the art. By aligning the sequences of polypeptides or nucleic acids, one skilled in the art can identify analogous portions or positions, using conserved and identical amino acid residues as guides. Further, one skilled in the art also can employ conserved amino acid or nucleotide residues as guides to find corresponding amino acid or nucleotide residues between and among human and non-human sequences. Corresponding positions also can be based on structural alignments, for example by using computer simulated alignments of protein structure. In other instances, corresponding regions can be identified. One skilled in the art also can employ conserved amino acid residues as guides to find corresponding amino acid residues between and among human and non-human sequences.

As used herein, a “property” of a polypeptide, such as an antibody, refers to any property exhibited by a polypeptide, including, but not limited to, binding specificity, structural configuration or conformation, protein stability, resistance to proteolysis, conformational stability, thermal tolerance, and tolerance to pH conditions. Changes in properties can alter an “activity” of the polypeptide. For example, a change in the binding specificity of the antibody polypeptide can alter the ability to bind an antigen, and/or various binding activities, such as affinity or avidity, or in vivo activities of the polypeptide.

As used herein, an “activity” or a “functional activity” of a polypeptide, such as an antibody, refers to any activity exhibited by the polypeptide. Such activities can be empirically determined. Exemplary activities include, but are not limited to, ability to interact with a biomolecule, for example, through antigen-binding, DNA binding, ligand binding, or dimerization, or enzymatic activity, for example, kinase activity or proteolytic activity. For an antibody (including antibody fragments), activities include, but are not limited to, the ability to specifically bind a particular antigen, affinity of antigen-binding (e.g., high or low affinity), avidity of antigen-binding (e.g., high or low avidity), on-rate, off-rate, effector functions, such as the ability to promote antigen neutralization or clearance, virus neutralization, and in vivo activities, such as the ability to prevent infection or invasion of a pathogen, or to promote clearance, or to penetrate a particular tissue or fluid or cell in the body. Activity can be assessed in vitro or in vivo using recognized assays, such as ELISA, flow cytometry, surface plasmon resonance or equivalent assays to measure on- or off-rate, immunohistochemistry and immunofluorescence histology and microscopy, cell-based assays, flow cytometry and binding assays (e.g., panning assays).

As used herein, “bind,” “bound” or grammatical variations thereof refers to the participation of a molecule in any attractive interaction with another molecule, resulting in a stable association in which the two molecules are in close proximity to one another. Binding includes, but is not limited to, non-covalent bonds, covalent bonds (such as reversible and irreversible covalent bonds), and includes interactions between molecules such as, but not limited to, proteins, nucleic acids, carbohydrates, lipids, and small molecules, such as chemical compounds including drugs.

As used herein, “antibody” refers to immunoglobulins and immunoglobulin fragments, whether natural or partially or wholly synthetic, such as recombinantly produced, including any fragment thereof containing at least a portion of the variable heavy chain and light region of the immunoglobulin molecule that is sufficient to form an antigen-binding site and, when assembled, to specifically bind an antigen. Hence, an antibody includes any protein having a binding domain that is homologous or substantially homologous to an immunoglobulin antigen-binding domain (antibody combining site). For example, an antibody refers to an antibody that contains two heavy chains (which can be denoted H and H′) and two light chains (which can be denoted L and L′), where each heavy chain can be a full-length immunoglobulin heavy chain or a portion thereof sufficient to form an antigen binding site (e.g., heavy chains include, but are not limited to, VH chains, VH-CH1 chains and VH-CH1-CH2-CH3 chains), and each light chain can be a full-length light chain or a portion thereof sufficient to form an antigen binding site (e.g., light chains include, but are not limited to, VL chains and VL-CL chains). Each heavy chain (H and H′) pairs with one light chain (L and L′, respectively). Typically, antibodies minimally include all or at least a portion of the variable heavy (VH) chain and/or the variable light (VL) chain. The antibody also can include all or a portion of the constant region.

For purposes herein, the term antibody includes full-length antibodies and portions thereof, including antibody fragments, such as anti-EGFR antibody fragments. Antibody fragments, include, but are not limited to, Fab fragments, Fab′ fragments, F(ab′)₂ fragments, a nanobody (such as a camelid antibody), fragments, disulfide-linked Fvs (dsFv), Fd fragments, Fd′ fragments, single-chain Fvs (scFv), single-chain Fabs (scFab), diabodies, anti-idiotypic (anti-Id) antibodies, or antigen-binding fragments of any of the above. Antibody also includes synthetic antibodies, recombinantly produced antibodies, multispecific antibodies (e.g., bispecific antibodies), human antibodies, non-human antibodies, humanized antibodies, chimeric antibodies, and intrabodies. Antibodies provided herein include members of any immunoglobulin class (e.g., IgG, IgM, IgD, IgE, IgA and IgY), any subclass (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2) or sub-subclass (e.g., IgG2a and IgG2b). Antibodies for human therapy generally are human antibodies or are humanized.

As used herein, “antibody fragment(s)” refers to (i) monovalent and monospecific antibody derivatives that contain the variable heavy and/or light chains or functional fragments of an antibody and lack an Fc part; and (ii) BiTE (tandem scFv), DARTs, diabodies and single-chain diabodies (scDB). Thus, an antibody fragment includes a/an: Fab, Fab′, scFab, scFv, Fv fragment, nanobody (see, e.g., antibodies derived from Camelus bactriamus, Calelus dromaderius, or Lama paccos) (see, e.g., U.S. Pat. No. 5,759,808; and Stijlemans et al. (2004) J. Biol. Chem. 279:1256-1261), VHH, dAb, minimal recognition unit, single-chain diabody (scDb), BiTE and DART. The recited antibody fragments have a molecular weight below 60 kDa.

As used herein, “nucleic acid” refers to at least two linked nucleotides or nucleotide derivatives, including a deoxyribonucleic acid (DNA) and a ribonucleic acid (RNA), joined together, typically by phosphodiester linkages. Also included in the term “nucleic acid” are analogs of nucleic acids such as peptide nucleic acid (PNA), phosphorothioate DNA, and other such analogs and derivatives or combinations thereof. Nucleic acids also include DNA and RNA derivatives containing, for example, a nucleotide analog or a “backbone” bond other than a phosphodiester bond, for example, a phosphotriester bond, a phosphoramidate bond, a phosphorothioate bond, a thioester bond, or a peptide bond (peptide nucleic acid). The term also includes, as equivalents, derivatives, variants and analogs of either RNA or DNA made from nucleotide analogs, single (sense or antisense) and double-stranded nucleic acids. Deoxyribonucleotides include deoxyadenosine, deoxycytidine, deoxyguanosine and deoxythymidine. For RNA, the uracil base is uridine.

As used herein, an isolated nucleic acid molecule is one which is separated from other nucleic acid molecules which are present in the natural source of the nucleic acid molecule. An “isolated” nucleic acid molecule, such as a cDNA molecule, can be substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. Exemplary isolated nucleic acid molecules provided herein include isolated nucleic acid molecules encoding an antibody or antigen-binding fragments provided.

As used herein, “operably linked” with reference to nucleic acid sequences, regions, elements or domains means that the nucleic acid regions are functionally related to each other. For example, a nucleic acid encoding a leader peptide can be operably linked to a nucleic acid encoding a polypeptide, whereby the nucleic acids can be transcribed and translated to express a functional fusion protein, wherein the leader peptide effects secretion of the fusion polypeptide. In some instances, the nucleic acid encoding a first polypeptide (e.g., a leader peptide) is operably linked to a nucleic acid encoding a second polypeptide and the nucleic acids are transcribed as a single mRNA transcript, but translation of the mRNA transcript can result in one of two polypeptides being expressed. For example, an amber stop codon can be located between the nucleic acid encoding the first polypeptide and the nucleic acid encoding the second polypeptide, such that, when introduced into a partial amber suppressor cell, the resulting single mRNA transcript can be translated to produce either a fusion protein containing the first and second polypeptides, or can be translated to produce only the first polypeptide. In another example, a promoter can be operably linked to nucleic acid encoding a polypeptide, whereby the promoter regulates or mediates the transcription of the nucleic acid.

As used herein, “synthetic,” with reference to, for example, a synthetic nucleic acid molecule or a synthetic gene or a synthetic peptide refers to a nucleic acid molecule or polypeptide molecule that is produced by recombinant methods and/or by chemical synthesis methods.

As used herein, the residues of naturally occurring α-amino acids are the residues of those 20 α-amino acids found in nature which are incorporated into protein by the specific recognition of the charged tRNA molecule with its cognate mRNA codon in humans.

As used herein, “polypeptide” refers to two or more amino acids covalently joined. The terms “polypeptide” and “protein” are used interchangeably herein.

As used herein, a “peptide” refers to a polypeptide that is from 2 to about or 40 amino acids in length.

As used herein, an “amino acid” is an organic compound containing an amino group and a carboxylic acid group. A polypeptide contains two or more amino acids. For purposes herein, amino acids contained in the antibodies provided include the twenty naturally-occurring amino acids (see Table below), non-natural amino acids, and amino acid analogs (e.g., amino acids wherein the α-carbon has a side chain). As used herein, the amino acids, which occur in the various amino acid sequences of polypeptides appearing herein, are identified according to their well-known, three-letter or one-letter abbreviations (see Table below). The nucleotides, which occur in the various nucleic acid molecules and fragments, are designated with the standard single-letter designations used routinely in the art.

As used herein, “amino acid residue” refers to an amino acid formed upon chemical digestion (hydrolysis) of a polypeptide at its peptide linkages. The amino acid residues described herein are generally in the “L” isomeric form. Residues in the “D” isomeric form can be substituted for any L-amino acid residue, as long as the desired functional property is retained by the polypeptide. NH₂ refers to the free amino group present at the amino terminus of a polypeptide. COOH refers to the free carboxy group present at the carboxyl terminus of a polypeptide. In keeping with standard polypeptide nomenclature described in J. Biol. Chem., 243:3557-59 (1968) and adopted at 37 C.F.R. §§ 1.821-1.822, abbreviations for amino acid residues are shown in the following Table:

Table of Correspondence SYMBOL 1-Letter 3-Letter AMINO ACID Y Tyr Tyrosine G Gly Glycine F Phe Phenylalanine M Met Methionine A Ala Alanine S Ser Serine I Ile Isoleucine L Leu Leucine T Thr Threonine V Val Valine P Pro Proline K Lys Lysine H His Histidine Q Gln Glutamine E Glu Glutamic acid Z Glx Glutamic Acid and/or Glutamine W Trp Tryptophan R Arg Arginine D Asp Aspartic acid N Asn Asparagine B Asx Aspartic Acid and/or Asparagine C Cys Cysteine X Xaa Unknown or other

All sequences of amino acid residues represented herein by a formula have a left to right orientation in the conventional direction of amino-terminus to carboxyl-terminus. The phrase “amino acid residue” is defined to include the amino acids listed in the above Table of Correspondence, modified, non-natural and unusual amino acids. A dash at the beginning or end of an amino acid residue sequence indicates a peptide bond to a further sequence of one or more amino acid residues or to an amino-terminal group such as NH₂ or to a carboxyl-terminal group such as COOH.

In a peptide or protein, suitable conservative substitutions of amino acids are known to those of skill in the art and generally can be made without altering a biological activity of a resulting molecule. Those of skill in the art recognize that, in general, single amino acid substitutions in non-essential regions of a polypeptide do not substantially alter biological activity (see, e.g., Watson et al., Molecular Biology of the Gene, 4th Edition, 1987, The Benjamin/Cummings Pub. Co., p. 224).

Such substitutions can be made in accordance with the exemplary substitutions set forth in the following Table:

Exemplary Conservative Amino Acid Substitutions

Exemplary Original Conservative residue substitution(s) Ala (A) Gly; Ser Arg (R) Lys Asn (N) Gln; His Cys (C) Ser Gln (Q) Asn Glu (E) Asp Gly (G) Ala; Pro His (H) Asn; Gln Ile (I) Leu; Val Leu (L) Ile; Val Lys (K) Arg; Gln; Glu Met (M) Leu; Tyr; Ile Phe (F) Met; Leu; Tyr Ser (S) Thr Thr (T) Ser Trp (W) Tyr Tyr (Y) Trp; Phe Val (V) Ile; Leu

Other substitutions also are permissible and can be determined empirically or in accord with other known conservative or non-conservative substitutions.

As used herein, “naturally occurring amino acids” refer to the 20 L-amino acids that occur in polypeptides.

As used herein, the term “non-natural amino acid” refers to an organic compound that has a structure similar to a natural amino acid but has been modified structurally to mimic the structure and reactivity of a natural amino acid. Non-naturally occurring amino acids thus include, for example, amino acids or analogs of amino acids other than the 20 naturally occurring amino acids and include, but are not limited to, the D-stereoisomers of amino acids. Exemplary non-natural amino acids are known to those of skill in the art, and include, but are not limited to, 2-Aminoadipic acid (Aad), 3-Aminoadipic acid (bAad), β-alanine/β-Amino-propionic acid (Bala), 2-Aminobutyric acid (Abu), 4-Aminobutyric acid/piperidinic acid (4Abu), 6-Aminocaproic acid (Acp), 2-Aminoheptanoic acid (Ahe), 2-Aminoisobutyric acid (Aib), 3-Aminoisobutyric acid (Baib), 2-Aminopimelic acid (Apm), 2,4-Diaminobutyric acid (Dbu), Desmosine (Des), 2,2′-Diaminopimelic acid (Dpm), 2,3-Diaminopropionic acid (Dpr), N-Ethylglycine (EtGly), N-Ethylasparagine (EtAsn), Hydroxylysine (Hyl), allo-Hydroxylysine (Ahyl), 3-Hydroxyproline (3Hyp), 4-Hydroxyproline (4Hyp), Isodesmosine (Ide), allo-Isoleucine (Aile), N-Methylglycine, sarcosine (MeGly), N-Methylisoleucine (MeIle), 6-N-Methyllysine (MeLys), N-Methylvaline (MeVal), Norvaline (Nva), Norleucine (Nle), and Ornithine (Orn).

As used herein, a DNA construct is a single or double stranded, linear or circular DNA molecule that contains segments of DNA combined and juxtaposed in a manner not found in nature. DNA constructs exist as a result of human manipulation, and include clones and other copies of manipulated molecules.

As used herein, a DNA segment is a portion of a larger DNA molecule having specified attributes. For example, a DNA segment encoding a specified polypeptide is a portion of a longer DNA molecule, such as a plasmid or plasmid fragment, which, when read from the 5′ to 3′ direction, encodes the sequence of amino acids of the specified polypeptide.

As used herein, the term polynucleotide means a single- or double-stranded polymer of deoxyribonucleotides or ribonucleotide bases read from the 5′ to the 3′ end. Polynucleotides include RNA and DNA, and can be isolated from natural sources, synthesized in vitro, or prepared from a combination of natural and synthetic molecules. The length of a polynucleotide molecule is given herein in terms of nucleotides (abbreviated “nt”) or base pairs (abbreviated “bp”). The term nucleotides is used for single- and double-stranded molecules where the context permits. When the term is applied to double-stranded molecules it is used to denote overall length and will be understood to be equivalent to the term base pairs. It will be recognized by those skilled in the art that the two strands of a double-stranded polynucleotide can differ slightly in length and that the ends thereof can be staggered; thus all nucleotides within a double-stranded polynucleotide molecule cannot be paired. Such unpaired ends will, in general, not exceed 20 nucleotides in length.

As used herein, production by recombinant methods refers means the use of the well-known methods of molecular biology for expressing proteins encoded by cloned DNA.

As used herein, “heterologous nucleic acid” is nucleic acid that encodes products (i.e., RNA and/or proteins) that are not normally produced in vivo by the cell in which it is expressed, or nucleic acid that is in a locus in which it does not normally occur, or that mediates or encodes mediators that alter expression of endogenous nucleic acid, such as DNA, by affecting transcription, translation, or other regulatable biochemical processes. Heterologous nucleic acid, such as DNA, also is referred to as foreign nucleic acid. Any nucleic acid, such as DNA, that one of skill in the art would recognize or consider as heterologous or foreign to the cell in which it is expressed, is herein encompassed by heterologous nucleic acid; heterologous nucleic acid includes exogenously added nucleic acid that is also expressed endogenously. Heterologous nucleic acid is generally not endogenous to the cell into which it is introduced, but has been obtained from another cell or prepared synthetically or is introduced into a genomic locus in which it does not occur naturally, or its expression is under the control of regulatory sequences or a sequence that differs from the natural regulatory sequence or sequences.

Examples of heterologous nucleic acid herein include, but are not limited to, nucleic acid that encodes RNAi, or an immunostimulatory protein, such as a cytokine, that confers or contributes to anti-tumor immunity in the tumor microenvironment, or that encodes an antibody, antibody fragment or other therapeutic product or therapeutic protein. In the immunostimulatory bacteria, the heterologous nucleic acid generally is encoded on the introduced plasmid, but it can be introduced into the genome of the bacterium, such as a promoter that alters expression of a bacterial product. Heterologous nucleic acid, such as DNA, includes nucleic acid that can, in some manner, mediate expression of DNA that encodes a therapeutic product, or it can encode a product, such as a peptide or RNA, that in some manner mediates, directly or indirectly, expression of a therapeutic product.

As used herein, cell therapy involves the delivery of cells to a subject to treat a disease or condition. The cells, which can be allogeneic or autologous, are modified ex vivo, such as by infection of cells with immunostimulatory bacteria provided herein, so that they deliver or express products when introduced to a subject.

As used herein, genetic therapy involves the transfer of heterologous nucleic acid, such as DNA, into certain cells, such as target cells, of a mammal, particularly a human, with a disorder or condition for which such therapy is sought. The nucleic acid, such as DNA, is introduced into the selected target cells in a manner such that the heterologous nucleic acid, such as DNA, is expressed and a therapeutic product(s) encoded thereby is produced. Genetic therapy can also be used to deliver nucleic acid encoding a gene product that replaces a defective gene or supplements a gene product produced by the mammal or the cell in which it is introduced. The introduced nucleic acid can encode a therapeutic compound, such as a growth factor or inhibitor thereof, or a tumor necrosis factor or inhibitor thereof, such as a receptor thereof, that is not normally produced in the mammalian host or that is not produced in therapeutically effective amounts or at a therapeutically useful time. The heterologous nucleic acid, such as DNA, encoding the therapeutic product, can be modified prior to introduction into the cells of the afflicted host in order to enhance or otherwise alter the product or expression thereof. Genetic therapy can also involve delivery of an inhibitor or repressor or other modulator of gene expression.

As used herein, “expression” refers to the process by which polypeptides are produced by transcription and translation of polynucleotides. The level of expression of a polypeptide can be assessed using any method known in art, including, for example, methods of determining the amount of the polypeptide produced from the host cell. Such methods can include, but are not limited to, quantitation of the polypeptide in the cell lysate by ELISA, Coomassie blue staining following gel electrophoresis, Lowry protein assay and Bradford protein assay.

As used herein, a “host cell” is a cell that is used to receive, maintain, reproduce and/or amplify a vector. A host cell also can be used to express the polypeptide encoded by the vector. The nucleic acid contained in the vector is replicated when the host cell divides, thereby amplifying the nucleic acids.

As used herein, a “vector” is a replicable nucleic acid from which one or more heterologous proteins, can be expressed when the vector is transformed into an appropriate host cell. Reference to a vector includes those vectors into which a nucleic acid encoding a polypeptide or fragment thereof can be introduced, typically by restriction digest and ligation. Reference to a vector also includes those vectors that contain nucleic acid encoding a polypeptide, such as a modified anti-EGFR antibody. The vector is used to introduce the nucleic acid encoding the polypeptide into the host cell for amplification of the nucleic acid or for expression/display of the polypeptide encoded by the nucleic acid. The vectors typically remain episomal, but can be designed to effect integration of a gene or portion thereof into a chromosome of the genome. Also contemplated are vectors that are artificial chromosomes, such as yeast artificial chromosomes and mammalian artificial chromosomes. Selection and use of such vehicles are well-known to those of skill in the art. A vector also includes “virus vectors” or “viral vectors.” Viral vectors are engineered viruses that are operatively linked to exogenous genes to transfer (as vehicles or shuttles) the exogenous genes into cells.

As used herein, an “expression vector” includes vectors capable of expressing DNA that is operatively linked with regulatory sequences, such as promoter regions, that are capable of effecting expression of such DNA fragments. Such additional segments can include promoter and terminator sequences, and optionally can include one or more origins of replication, one or more selectable markers, an enhancer, a polyadenylation signal, and the like. Expression vectors are generally derived from plasmid or viral DNA, or can contain elements of both. Thus, an expression vector refers to a recombinant DNA or RNA construct, such as a plasmid, a phage, recombinant virus or other vector that, upon introduction into an appropriate host cell, results in expression of the cloned DNA. Appropriate expression vectors are well-known to those of skill in the art and include those that are replicable in eukaryotic cells and/or prokaryotic cells and those that remain episomal or those which integrate into the host cell genome.

As used herein, “primary sequence” refers to the sequence of amino acid residues in a polypeptide or the sequence of nucleotides in a nucleic acid molecule.

As used herein, “sequence identity” refers to the number of identical or similar amino acids or nucleotide bases in a comparison between a test and a reference polypeptide or polynucleotide. Sequence identity can be determined by sequence alignment of nucleic acid or protein sequences to identify regions of similarity or identity. For purposes herein, sequence identity is generally determined by alignment to identify identical residues. The alignment can be local or global. Matches, mismatches and gaps can be identified between compared sequences. Gaps are null amino acids or nucleotides inserted between the residues of aligned sequences so that identical or similar characters are aligned. Generally, there can be internal and terminal gaps. When using gap penalties, sequence identity can be determined with no penalty for end gaps (e.g., terminal gaps are not penalized). Alternatively, sequence identity can be determined without taking into account gaps as the number of identical positions/length of the total aligned sequence×100.

As used herein, a “global alignment” is an alignment that aligns two sequences from beginning to end, aligning each letter in each sequence only once. An alignment is produced, regardless of whether or not there is similarity or identity between the sequences. For example, 50% sequence identity based on “global alignment” means that in an alignment of the full sequence of two compared sequences each of 100 nucleotides in length, 50% of the residues are the same. It is understood that global alignment also can be used in determining sequence identity even when the length of the aligned sequences is not the same. The differences in the terminal ends of the sequences will be taken into account in determining sequence identity, unless the “no penalty for end gaps” is selected. Generally, a global alignment is used on sequences that share significant similarity over most of their length. Exemplary algorithms for performing global alignment include the Needleman-Wunsch algorithm (Needleman et al. (1970) J. Mol. Biol. 48: 443). Exemplary programs for performing global alignment are publicly available and include the Global Sequence Alignment Tool available at the National Center for Biotechnology Information (NCBI) website (ncbi.nlm.nih.gov/), and the program available at deepc2.psi.iastate.edu/aat/align/align.html.

As used herein, a “local alignment” is an alignment that aligns two sequences, but only aligns those portions of the sequences that share similarity or identity. Hence, a local alignment determines if sub-segments of one sequence are present in another sequence. If there is no similarity, no alignment will be returned. Local alignment algorithms include BLAST or Smith-Waterman algorithm (Adv. Appl. Math. 2: 482 (1981)). For example, 50% sequence identity based on “local alignment” means that in an alignment of the full sequence of two compared sequences of any length, a region of similarity or identity of 100 nucleotides in length has 50% of the residues that are the same in the region of similarity or identity.

For purposes herein, sequence identity can be determined by standard alignment algorithm programs used with default gap penalties established by each supplier. Default parameters for the GAP program can include: (1) a unary comparison matrix (containing a value of 1 for identities and 0 for non-identities) and the weighted comparison matrix of Gribskov et al. (1986) Nucl. Acids Res. 14: 6745, as described by Schwartz and Dayhoff, eds., Atlas of Protein Sequence and Structure, National Biomedical Research Foundation, pp. 353-358 (1979); (2) a penalty of 3.0 for each gap and an additional 0.10 penalty for each symbol in each gap; and (3) no penalty for end gaps. Whether any two nucleic acid molecules have nucleotide sequences or any two polypeptides have amino acid sequences that are at least 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% “identical,” or other similar variations reciting a percent identity, can be determined using known computer algorithms based on local or global alignment (see e.g., wikipedia.org/wiki/Sequence_alignment_software, providing links to dozens of known and publicly available alignment databases and programs). Generally, for purposes herein sequence identity is determined using computer algorithms based on global alignment, such as the Needleman-Wunsch Global Sequence Alignment tool available from NCBI/BLAST (blast.ncbi.nlm.nih.gov/Blast.cgi?CMD=Web&Page_TYPE=BlastHome); LAlign (William Pearson implementing the Huang and Miller algorithm (Adv. Appl. Math. (1991) 12:337-357)); and program from Xiaoqui Huang available at deepc2.psi.iastate.edu/aat/align/align.html. Typically, the full-length sequence of each of the compared polypeptides or nucleotides is aligned across the full-length of each sequence in a global alignment. Local alignment also can be used when the sequences being compared are substantially the same length.

Therefore, as used herein, the term “identity” represents a comparison or alignment between a test and a reference polypeptide or polynucleotide. In one non-limiting example, “at least 90% identical to” refers to percent identities from 90 to 100% relative to the reference polypeptide or polynucleotide. Identity at a level of 90% or more is indicative of the fact that, assuming for exemplification purposes a test and reference polypeptide or polynucleotide length of 100 amino acids or nucleotides are compared, no more than 10% (i.e., 10 out of 100) of amino acids or nucleotides in the test polypeptide or polynucleotide differ from those of the reference polypeptide. Similar comparisons can be made between a test and reference polynucleotides. Such differences can be represented as point mutations randomly distributed over the entire length of an amino acid sequence or they can be clustered in one or more locations of varying length up to the maximum allowable, e.g., 10/100 amino acid difference (approximately 90% identity). Differences also can be due to deletions or truncations of amino acid residues. Differences are defined as nucleic acid or amino acid substitutions, insertions or deletions. Depending on the length of the compared sequences, at the level of homologies or identities above about 85-90%, the result can be independent of the program and gap parameters set; such high levels of identity can be assessed readily, often without relying on software.

As used herein, “disease or disorder” refers to a pathological condition in an organism resulting from a cause or condition including, but not limited to, infections, acquired conditions, and genetic conditions, and that is characterized by identifiable symptoms.

As used herein, “treating” a subject with a disease or condition means that the subject's symptoms are partially or totally alleviated, or remain static following treatment.

As used herein, treatment refers to any effects that ameliorate symptoms of a disease or disorder. Treatment encompasses prophylaxis, therapy and/or cure.

Treatment also encompasses any pharmaceutical use of any immunostimulatory bacterium or composition provided herein.

As used herein, prophylaxis refers to prevention of a potential disease and/or a prevention of worsening of symptoms or progression of a disease.

As used herein, “prevention” or prophylaxis, and grammatically equivalent forms thereof, refers to methods in which the risk or probability of developing a disease or condition is reduced.

As used herein, a “pharmaceutically effective agent” includes any therapeutic agent or bioactive agents, including, but not limited to, for example, anesthetics, vasoconstrictors, dispersing agents, and conventional therapeutic drugs, including small molecule drugs and therapeutic proteins.

As used herein, a “therapeutic effect” means an effect resulting from treatment of a subject that alters, typically improves or ameliorates, the symptoms of a disease or condition or that cures a disease or condition.

As used herein, a “therapeutically effective amount” or a “therapeutically effective dose” refers to the quantity of an agent, compound, material, or composition containing a compound that is at least sufficient to produce a therapeutic effect following administration to a subject. Hence, it is the quantity necessary for preventing, curing, ameliorating, arresting or partially arresting a symptom of a disease or disorder.

As used herein, “therapeutic efficacy” refers to the ability of an agent, compound, material, or composition containing a compound to produce a therapeutic effect in a subject to whom the agent, compound, material, or composition containing a compound has been administered.

As used herein, a “prophylactically effective amount” or a “prophylactically effective dose” refers to the quantity of an agent, compound, material, or composition containing a compound that when administered to a subject, will have the intended prophylactic effect, e.g., preventing or delaying the onset, or reoccurrence, of disease or symptoms, reducing the likelihood of the onset, or reoccurrence, of disease or symptoms, or reducing the incidence of viral infection. The full prophylactic effect does not necessarily occur by administration of one dose, and can occur only after administration of a series of doses. Thus, a prophylactically effective amount can be administered in one or more administrations.

As used herein, amelioration of the symptoms of a particular disease or disorder by a treatment, such as by administration of a pharmaceutical composition or other therapeutic, refers to any lessening, whether permanent or temporary, lasting or transient, of the symptoms that can be attributed to or associated with administration of the composition or therapeutic.

As used herein, an “anti-cancer agent” refers to any agent that is destructive or toxic to malignant cells and tissues. For example, anti-cancer agents include agents that kill cancer cells or otherwise inhibit or impair the growth of tumors or cancer cells. Exemplary anti-cancer agents are chemotherapeutic agents.

As used herein “therapeutic activity” refers to the in vivo activity of a therapeutic polypeptide. Generally, the therapeutic activity is the activity that is associated with treatment of a disease or condition.

As used herein, the term “subject” refers to an animal, including a mammal, such as a human being.

As used herein, a patient refers to a human subject.

As used herein, animal includes any animal, such as, but not limited to, primates including humans, gorillas and monkeys; rodents, such as mice and rats; fowl, such as chickens; ruminants, such as goats, cows, deer, sheep; pigs and other animals. Non-human animals exclude humans as the contemplated animal. The polypeptides provided herein are from any source, animal, plant, prokaryotic and fungal. Most polypeptides are of animal origin, including mammalian origin.

As used herein, a “composition” refers to any mixture. It can be a solution, suspension, liquid, powder, paste, aqueous, non-aqueous or any combination thereof.

As used herein, a “combination” refers to any association between or among two or more items. The combination can be two or more separate items, such as two compositions or two collections, a mixture thereof, such as a single mixture of the two or more items, or any variation thereof. The elements of a combination are generally functionally associated or related.

As used herein, combination therapy refers to administration of two or more different therapeutics. The different therapeutics or therapeutic agents can be provided and administered separately, sequentially, intermittently, or can be provided in a single composition.

As used herein, a kit is a packaged combination that optionally includes other elements, such as additional reagents and instructions for use of the combination or elements thereof, for a purpose including, but not limited to, activation, administration, diagnosis, and assessment of a biological activity or property.

As used herein, a “unit dose form” refers to physically discrete units suitable for human and animal subjects and packaged individually as is known in the art.

As used herein, a “single dosage formulation” refers to a formulation for direct administration.

As used herein, a multi-dose formulation refers to a formulation that contains multiple doses of a therapeutic agent and that can be directly administered to provide several single doses of the therapeutic agent. The doses can be administered over the course of minutes, hours, weeks, days or months. Multi-dose formulations can allow dose adjustment, dose-pooling and/or dose-splitting. Because multi-dose formulations are used over time, they generally contain one or more preservatives to prevent microbial growth.

As used herein, an “article of manufacture” is a product that is made and sold. As used throughout this application, the term is intended to encompass any of the compositions provided herein contained in articles of packaging.

As used herein, a “fluid” refers to any composition that can flow. Fluids thus encompass compositions that are in the form of semi-solids, pastes, solutions, aqueous mixtures, gels, lotions, creams and other such compositions.

As used herein, an isolated or purified polypeptide or protein (e.g., an isolated antibody or antigen-binding fragment thereof) or biologically-active portion thereof (e.g., an isolated antigen-binding fragment) is substantially free of cellular material or other contaminating proteins from the cell or tissue from which the protein is derived, or substantially free from chemical precursors or other chemicals when chemically synthesized. Preparations can be determined to be substantially free if they appear free of readily detectable impurities as determined by standard methods of analysis, such as thin layer chromatography (TLC), gel electrophoresis and high performance liquid chromatography (HPLC), used by those of skill in the art to assess such purity, or sufficiently pure such that further purification does not detectably alter the physical and chemical properties, such as enzymatic and biological activities, of the substance. Methods for purification of the compounds to produce substantially chemically pure compounds are known to those of skill in the art. A substantially chemically pure compound, however, can be a mixture of stereoisomers. In such instances, further purification might increase the specific activity of the compound. As used herein, a “cellular extract” or “lysate” refers to a preparation or fraction which is made from a lysed or disrupted cell.

As used herein, a “control” refers to a sample that is substantially identical to the test sample, except that it is not treated with a test parameter, or, if it is a plasma sample, it can be from a normal volunteer not affected with the condition of interest. A control also can be an internal control.

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a polypeptide, comprising “an immunoglobulin domain” includes polypeptides with one or a plurality of immunoglobulin domains.

As used herein, the term “or” is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive.

As used herein, ranges and amounts can be expressed as “about” a particular value or range. About also includes the exact amount. Hence “about 5 amino acids” means “about 5 amino acids” and also “5 amino acids.”

As used herein, “optional” or “optionally” means that the subsequently described event or circumstance does or does not occur and that the description includes instances where said event or circumstance occurs and instances where it does not. For example, an optionally variant portion means that the portion is variant or non-variant.

As used herein, the abbreviations for any protective groups, amino acids and other compounds, are, unless indicated otherwise, in accord with their common usage, recognized abbreviations, or the IUPAC-IUB Commission on Biochemical Nomenclature (see, Biochem. (1972) 11(9):1726-1732).

For clarity of disclosure, and not by way of limitation, the detailed description is divided into the subsections that follow.

B. OVERVIEW OF THE IMMUNOSTIMULATORY BACTERIA

Provided are modified bacteria, called immunostimulatory bacteria herein that accumulate and/or replicate in (i.e., colonize) tumors, tumor-resident immune cells and/or the tumor microenvironment (TME); and/or induce less cell death in tumor-resident immune cells; and/or encode therapeutic products, such as anti-tumor agents, immunostimulatory proteins, and inhibitory RNAs (RNAi), such as shRNAs and microRNAs (miRNAs), that target genes whose inhibition, suppression or silencing effects tumor therapy. Strains of bacteria for modification are any suitable for therapeutic use. The modified immunostimulatory bacteria provided herein are for uses and for methods for treating cancer. The bacteria are modified for such uses and methods.

The immunostimulatory bacteria provided herein are modified by deletion or modification of bacterial genes to attenuate their inflammatory responses, increase their tolerability, increase their resistance to complement, increase their infectivity of, accumulation in or colonization of tumors, tumor-resident immune cells and/or the TME, decrease their induction of immune cell death (e.g., decrease pyroptosis), and to enhance the anti-tumor immune responses in hosts treated with the bacteria. The modifications also can be in genes encoded on a plasmid in the bacteria. For example, the bacteria can be auxotrophic for adenosine, or adenosine and adenine, and plasmids encoding therapeutic products, such as immunostimulatory proteins, antibodies, or RNAi that inhibit immune checkpoint genes in the host are included in the bacteria. Attenuation of the inflammatory responses to the bacteria can be effected by deletion of the msbB gene, which decreases TNF-alpha in the host, and/or knocking out flagellin genes and/or deletion/mutation of pagP. The bacteria are modified to stimulate host anti-tumor activity, for example, by adding plasmids encoding immunostimulatory proteins such as cytokines, chemokines and co-stimulatory molecules, or RNAi that target host immune checkpoints, and by adding nucleic acid with CpGs/CpG motifs.

Bacterial strains can be attenuated strains, or strains that are attenuated by standard methods, or that, by virtue of the modifications provided herein, are attenuated in that their ability to colonize is limited primarily to immunoprivilaged tissues and organs, particularly immune and tumor cells, including solid tumors. Bacteria include, but are not limited to, for example, strains of Salmonella, Shigella, Listeria, E. coli, and Bifidobacteriae. For example, species include Shigella sonnei, Shigella flexneri, Shigella dysenteriae, Listeria monocytogenes, Salmonella typhi, Salmonella typhimurium, Salmonella gallinarum, and Salmonella enteritidis. Other suitable bacterial species include Rickettsia, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Vibrio, Bacillus, and Erysipelothrix. For example, Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia tsutsugamuchi, Rickettsia mooseri, Rickettsia sibirica, Bordetella bronchiseptica, Neisseria meningitidis, Neisseria gonorrhoeae, Aeromonas eucrenophila, Aeromonas salmonicida, Francisella tularensis, Corynebacterium pseudotuberculosis, Citrobacter freundii, Chlamydia pneumoniae, Haemophilus somnus, Brucella abortus, Mycobacterium intracellulare, Legionella pneumophila, Rhodococcus equi, Pseudomonas aeruginosa, Helicobacter mustelae, Vibrio cholerae, Bacillus subtilis, Erysipelothrix rhusiopathiae, Yersinia enterocolitica, Rochalimaea quintana, and Agrobacterium tumerfacium.

The bacteria accumulate by virtue of one or more properties, including, diffusion, migration and chemotaxis to immunoprivileged tissues or organs or environments, environments that provide nutrients or other molecules for which they are auxotrophic, and/or environments that contain replicating cells that provide environments suitable for entry and replication of the bacteria. The immunostimulatory bacteria provided herein and species that effect such therapy include species of Salmonella, Listeria, and E. coli.

The bacteria contain plasmids that encode a therapeutic protein, such as an immunostimulatory protein or an immune checkpoint inhibitor or other immune stimulating or immune-suppression blocking product. Products include antibodies, such as antibody fragments, and nanobodies, RNAi, such as one or more short hairpin (sh) RNA construct(s), microRNAs, or other RNAi modalities, whose expression inhibits or disrupts or suppresses the expression of targeted genes, or otherwise increases immune responses or decreases immune suppression. The therapeutic products are expressed under control of a eukaryotic promoter, such as an RNA polymerase (RNAP) II or III promoter. Typically, RNAPIII (also referred to as POLIII) promoters are constitutive, and RNAPII (also referred to as POLII) can be regulated. In some examples, the shRNAs target the gene TREX1, to inhibit its expression.

In some embodiments, the plasmids can encode a plurality of therapeutic products, including immunostimulatory proteins, such as cytokines, and RNAi molecules, such as shRNAs, and antibodies, including nanobodies, that inhibit two or more immune checkpoint genes, such as TREX1, PD-L1, VISTA, SIRPα, CTNNB1, TGF-beta, CD47, and/or VEGF and any others known to those of skill in the art. Where a plurality of therapeutic products are encoded, expression of each generally is under control of a different promoter.

Among the bacteria provided herein, are bacteria that are modified so that they are auxotrophic for adenosine. This can be achieved by modification or deletion of genes involved in purine synthesis, metabolism, or transport. For example, disruption of the tsx gene in Salmonella species, such as Salmonella typhi, results in adenosine auxotrophy. Adenosine is immunosuppressive and accumulates to high concentrations in tumors; auxotrophy for adenosine improves the anti-tumor activity of the bacteria because the bacteria selectively replicate in tissues rich in adenosine.

Also provided are bacteria that are modified so that they have a defective asd gene. These bacteria for use in vivo are modified to include carrying a functional asd gene on the introduced plasmid; this maintains selection for the plasmid so that an antibiotic-based plasmid maintenance/selection system is not needed. Also provided is the use of asd defective strains that do not contain a functional asd gene on a plasmid, and are thus engineered to be autolytic in the host.

Also provided are bacteria that are modified so that they are incapable of producing flagella. This can be achieved by modifying the bacteria by deleting the genes that encode the flagellin subunits. The modified bacteria lacking flagellin are less inflammatory and therefore better tolerated, and induce a more potent anti-tumor response.

Also provided are bacteria that are modified to produce listeriolysin O (LLO), which improves plasmid delivery in phagocytic cells.

Also provided are bacteria modified to carry a low copy, CpG-containing plasmid. The plasmid further can include other modifications, and can encode therapeutic products, such as immunostimulatory proteins, antibodies and fragments thereof, and RNAi.

The bacteria also can be modified to grow in a manner such that the bacteria, if a Salmonella species, expresses less of the toxic SPI-1 (Salmonella pathogenicity island-1) genes. In Salmonella, genes responsible for virulence, invasion, survival, and extra intestinal spread are located in Salmonella pathogenicity islands (SPIs).

The bacteria include plasmids that encode RNAi, such as shRNA or microRNA, that inhibits checkpoints, such as PD-L1 or TREX1 only, or TREX1 and one or more of a second immune checkpoint. The bacteria can be further modified for other desirable traits, including for selection of plasmid maintenance, particularly for selection without antibiotics, for preparation of the strains. The immunostimulatory bacteria optionally can encode therapeutic polypeptides, including anti-tumor therapeutic polypeptides and agents.

Exemplary of the immunostimulatory bacteria provided herein are species of Salmonella. Exemplary of bacteria for modification as described herein are engineered strains of Salmonella typhimurium, such as strain YS1646 (ATCC Catalog #202165; also referred to as VNP20009, see, International PCT Application Publication No. WO 99/13053) that is engineered with plasmids to complement an asd gene knockout and antibiotic-free plasmid maintenance.

Modified immunostimulatory bacterial strains that are rendered auxotrophic for adenosine are provided herein, as are pharmaceutical compositions containing such strains, formulated for administration to a subject, such as a human, for use in methods of treating tumors and cancers.

Also provided are methods or uses of the immunostimulatory bacteria or pharmaceutical compositions containing the bacteria, wherein the treatment comprises combination therapy, in which a second anti-cancer agent or treatment is administered. The second anti-cancer agent or treatment can be administered before, concomitantly with, after, or intermittently with, the immunostimulatory bacteria or pharmaceutical composition, and includes immunotherapy, such as an antibody or antibody fragment; oncolytic virus therapy; radiation/radiotherapy; and chemotherapy. The immunotherapy can comprise, for example, administration of an anti-PD-1, or anti-PD-L1 or anti-CTLA4, or anti-IL6, or anti-VEGF, or anti-VEGFR, or anti-VEGFR2 antibody, or a fragment thereof. Combination therapy also can include surgery.

The engineered immunostimulatory bacteria provided herein contain multiple synergistic modalities to induce immune re-activation of cold tumors and to promote tumor antigen-specific immune responses, while inhibiting immune checkpoint pathways that the tumor utilizes to subvert and evade durable anti-tumor immunity. Improved tumor targeting through adenosine auxotrophy and enhanced vascular disruption have improved potency, while localizing the inflammation to limit systemic cytokine exposure and the autoimmune toxicities observed with other immunotherapy modalities. Exemplary of the bacteria so-modified are S. typhimurium strains, including such modifications of the strain YS1646, particularly asd⁻ strains.

For example, as provided herein, are immunostimulatory bacteria that provide for shRNA-mediated gene disruption of PD-L1. It has been shown in mice that gene disruption of PD-L1 can improve tumor colonization. It has been shown, for example, that S. typhimurium infection in PD-L1 knockout mice, results in a 10-fold higher bacterial load than in wild-type mice (see, Lee et al. (2010) J. Immunol. 185:2442-2449). Hence, PD-L1 is protective against S. typhimurium infection. Provided herein are immunostimulatory bacteria, such as S. typhimurium, carrying plasmids capable of RNAi-mediated gene knockdown of TREX1, PD-L1, or of PD-L1 and TREX1. Such bacteria provide anti-tumor effects due to the combination of two independent pathways that lead to enhanced and sustained anti-tumor immune responses in a single therapy.

C. CANCER IMMUNOTHERAPEUTICS

The immunosuppressive milieu found within the tumor microenvironment (TME) is a driver of tumor initiation and progression. Cancers emerge after the immune system fails to control and contain tumors. Multiple tumor-specific mechanisms create tumor environments wherein the immune system is forced to tolerate tumors and their cells instead of eliminating them. The goal of cancer immunotherapy is to rescue the immune system's natural ability to eliminate tumors. Acute inflammation associated with microbial infection has been observationally linked with the spontaneous elimination of tumors for centuries.

1. Immunotherapies

Several clinical cancer immunotherapies have sought to perturb the balance of immune suppression towards anti-tumor immunity. Strategies to stimulate immunity through directly administering cytokines such as IL-2 and IFN-α have seen modest clinical responses in a minority of patients, while inducing serious systemic inflammation-related toxicities (Sharma et al. (2011) Nat. Rev. Cancer 11:805-812). The immune system has evolved several checks and balances to limit autoimmunity, such as upregulation of programmed cell death protein 1 (PD-1) on T cells and its binding to its cognate ligand, programmed death-ligand 1 (PD-L1), which is expressed on both antigen presenting cells (APCs) and tumor cells. The binding of PD-L1 to PD-1 interferes with CD8⁺ T cell signaling pathways, impairing the proliferation and effector function of CD8⁺ T cells, and inducing T cell tolerance. PD-1 and PD-L1 are two examples of numerous inhibitory “immune checkpoints,” which function by downregulating immune responses. Other inhibitory immune checkpoints include cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), signal regulatory protein α (SIRPα), V-domain Ig suppressor of T cell activation (VISTA), programmed death-ligand 2 (PD-L2), indoleamine 2,3-dioxygenase (IDO) 1 and 2, lymphocyte-activation gene 3 (LAG3), Galectin-9, T cell immunoreceptor with Ig and ITIM domains (TIGIT), T cell immunoglobulin and mucin-domain containing-3 (TIM-3, also known as hepatitis A virus cellular receptor 2 (HAVCR2)), herpesvirus entry mediator (HVEM), CD39, CD73, B7-H3 (also known as CD276), B7-H4, CD47, CD48, CD80 (B7-1), CD86 (B7-2), CD155, CD160, CD244 (2B4), B- and T-lymphocyte attenuator (BTLA, or CD272) and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1, or CD66a).

Antibodies designed to block immune checkpoints, such as anti-PD-1 (for example, pembrolizumab, nivolumab) and anti-PD-L1 (for example, atezolizumab, avelumab, durvalumab), have had durable success in preventing T cell anergy and breaking immune tolerance. Only a fraction of treated patients demonstrate clinical benefit, and those that do often present with autoimmune-related toxicities (see, e.g., Ribas (2015) N Engl J Med 373:1490-1492; Topalian et al. (2012) N Engl J Med 366:2443-2454). This is further evidence for the need for therapies, provided herein, that are more effective and less toxic.

Another checkpoint blockade strategy inhibits the induction of CTLA-4 on T cells, which binds to and inhibits co-stimulatory receptors on APCs, such as CD80 or CD86, out-competing the co-stimulatory cluster differentiation 28 (CD28), which binds the same receptors, but with a lower affinity. This blocks the stimulatory signal from CD28, while the inhibitory signal from CTLA-4 is transmitted, preventing T cell activation (see, Phan et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100:8372-8377). Anti-CTLA-4 therapy (for example, ipilimumab) have clinical success and durability in some patients, whilst exhibiting an even greater incidence of severe immune-related adverse events (see, e.g., Hodi et al. (2010) N. Engl. J. Med. 363:711-723; Schadendorf et al. (2015) J. Clin. Oncol. 33:1889-1894). It also has been shown that tumors develop resistance to anti-immune checkpoint antibodies, highlighting the need for more durable anticancer therapies, and provided herein.

2. Adoptive Immunotherapies

In seeking to reactivate a cold tumor to become more immunogenic, a class of immunotherapies known as adoptive cell therapy (ACT) encompasses a variety of strategies to harness immune cells and reprogram them to have anti-tumor activity (Zielinski et al. (2011) Immunol. Rev. 240:40-51). Dendritic cell-based therapies introduce genetically engineered dendritic cells (DCs) with more immune-stimulatory properties. These therapies have not been successful because they fail to break immune tolerance to cancer (see, e.g., Rosenberg et al. (2004) Nat. Med. 10(12):1279). A method using whole irradiated tumor cells containing endogenous tumor antigens and granulocyte macrophage colony-stimulating factor (GM-CSF) to stimulate DC recruitment, known as GVAX, similarly failed in the clinic due to the lack of ability to break tumor tolerance (Copier et al. (2010) Curr. Opin. Mol. Ther. 12:14-20). A separate autologous cell-based therapy, Sipuleucel-T (Provenge), was FDA approved in 2010 for castration-resistant prostate cancer. It utilizes APCs retrieved from the patient and re-armed to express prostatic acid phosphatase (PAP) antigen to stimulate a T cell response, then re-introduced following lymphablation. Unfortunately, its broader adoption has been limited by low observed objective response rates and high costs, and its use is limited to only the early stages of prostate cancer (Anassi et al. (2011) P T 36(4):197-202). Similarly, autologous T cell therapies (ATCs) harvest a patient's own T cells and reactivate them ex vivo to overcome tumor tolerance, then reintroduce them to the patient following lymphablation. ATCs have had limited clinical success, and only in melanoma, while generating serious safety and feasibility issues that limit their utility (Yee (2013) Clin. Cancer Res. 19:4550-4552).

Chimeric antigen receptor T cell (CAR-T) therapies are T cells harvested from patients that have been re-engineered to express a fusion protein between the T cell receptor and an antibody Ig variable extracellular domain. This confers upon them the antigen-recognition properties of antibodies with the cytolytic properties of activated T cells (Sadelain (2015) J. Clin. Invest. 125:3392-3400). Success has been limited to B cell and hematopoietic malignancies, at the cost of deadly immune-related adverse events (Jackson et al. (2016) Nat. Rev. Clin. Oncol. 13:370-383). Tumors can also mutate to escape recognition by a target antigen, including CD19 (Ruella et al., (2016) Comput. Struct. Biotechnol. J. 14: 357-362) and EGFRvIII (O'Rourke et al. (2017) Sci. Transl. Med. (399):eaaa0984), thereby fostering immune escape. In addition, while CAR-T therapies are approved and are approved in the context of hematological malignancies, they face a significant hurdle for feasibility to treat solid tumors: overcoming the highly immunosuppressive nature of the solid tumor microenvironment. A number of additional modifications to existing CAR-T therapies will be required to potentially provide feasibility against solid tumors (Kakarla et al. (2014) Cancer J. 20(2):151-155). When the safety of CAR-Ts is significantly improved and their efficacy expanded to solid tumors, the feasibility and costs associated with these labor-intensive therapies will continue to limit their broader adoption.

3. Cancer Vaccines and Oncolytic Viruses

Cold tumors lack T cell and dendritic cell (DC) infiltration, and are non-T-cell-inflamed (Sharma et al. (2017) Cell 9; 168(4):707-723). In seeking to reactivate a cold tumor to become more immunogenic, another class of immunotherapies harness microorganisms that can accumulate in tumors, either naturally or by virtue of engineering. These include viruses designed to stimulate the immune system to express tumor antigens, thereby activating and reprogramming the immune system to reject the tumor. Virally-based cancer vaccines have largely failed clinically for a number of factors, including pre-existing or acquired immunity to the viral vector itself, as well as a lack of sufficient immunogenicity to the expressed tumor antigens (Larocca et al. (2011) Cancer J. 17(5):359-371). Lack of proper adjuvant activation of APCs has also hampered other non-viral vector cancer vaccines, such as DNA vaccines. Oncolytic viruses, in contrast, seek to preferentially replicate in dividing tumor cells over healthy tissue, whereupon subsequent tumor cell lysis leads to immunogenic tumor cell death and further viral dissemination. The oncolytic virus Talimogene laherparepvec (T-VEC), which uses a modified herpes simplex virus in combination with the DC-recruiting cytokine GM-CSF, is FDA approved for metastatic melanoma (Bastin et al. (2016) Biomedicines 4(3):21). While demonstrating clinical benefit in some melanoma patients, and with fewer immune toxicities than with other immunotherapies, the intratumoral route of administration and manufacturing conditions have been limiting, as well as its lack of distal tumor efficacy and broader application to other tumor types. Other oncolytic virus (OV)-based vaccines, such as those utilizing paramyxovirus, reovirus and picornavirus, among others, have met with similar limitations in inducing systemic anti-tumor immunity (Chiocca et al. (2014) Cancer Immunol. Res. 2(4):295-300). Systemic administration of oncolytic viruses presents unique challenges. Upon I.V. administration, the virus is rapidly diluted, thus requiring high titers that can lead to hepatotoxicity. Further, if pre-existing immunity exists, the virus is rapidly neutralized in the blood, and acquired immunity then restricts repeat dosing (Maroun et al. (2017) Future Virol. 12(4):193-213).

Of the limitations of virally-based vaccine vectors and oncolytic viruses, the greatest limitations can be the virus itself. Viral antigens have strikingly higher affinities to human T cell receptors (TCR) compared to tumor antigens (Aleksic et al. (2012) Eur J. Immunol. 42(12):3174-3179). Tumor antigens, presented alongside of viral vector antigens by MHC-1 on the surface of even highly activated APCs, will be outcompeted for binding to TCRs, resulting in very poor antigen-specific anti-tumor immunity. A tumor-targeting immunostimulatory vector, as provided herein, that does not itself provide high affinity T cell epitopes can circumvent these limitations.

D. BACTERIAL CANCER IMMUNOTHERAPY

1. Bacterial Therapies

The recognition that bacteria have anticancer activity goes back to the 1800s, when several physicians observed regression of tumors in patients infected with Streptococcus pyogenes. William Coley began the first study utilizing bacteria for the treatment of end stage cancers, and developed a vaccine composed of S. pyogenes and Serratia marcescens, which was successfully used to treat a variety of cancers, including sarcomas, carcinomas, lymphomas and melanomas. Since then, a number of bacteria, including species of Clostridium, Mycobacterium, Bifidobacterium, Listeria, such as, L. monocytogenes, and Escherichia species, have been studied as sources of anti-cancer vaccines (see, e.g., International PCT Application Publication No. WO 1999/013053; International PCT Application Publication No. WO 2001/025399; Bermudes et al. (2002) Curr. Opin. Drug Discov. Devel. 5:194-199; Patyar et al. (2010) Journal of Biomedical Science 17:21; Pawelek et al. (2003) Lancet Oncol. 4:548-556).

Bacteria can infect animal and human cells, and some possess the innate ability to deliver DNA into the cytosol of cells, and these are candidate vectors for gene therapy. Bacteria also are suitable for therapy because they can be administered orally, they propagate readily in vitro and in vivo, and they can be stored and transported in a lyophilized state. Bacterial genetics are readily manipulated, and the complete genomes for many strains have been fully characterized (Felgner et al. (2016) mbio 7(5):e01220-16). As a result, bacteria have been used to deliver and express a wide variety of genes, including those that encode cytokines, angiogenesis inhibitors, toxins and prodrug-converting enzymes. Salmonella, for example, has been used to express immune-stimulating molecules like IL-18 (Loeffler et al. (2008) Cancer Gene Ther. 15(12):787-794), LIGHT (Loeffler et al. (2007) Proc. Natl. Acad. Sci. USA 104(31): 12879-12883), and Fas ligand (Loeffler et al. (2008) J. Natl. Cancer Inst. 100:1113-1116) in tumors. Bacterial vectors also are cheaper and easier to produce than viral vectors, and bacterial delivery is favorable over viral delivery because it can be quickly eliminated by antibiotics if necessary, rendering it a safer alternative.

To be used, however, the strains themselves must not be pathogenic or are not pathogenic after modification for use as a therapeutic. For example, in the treatment of cancer, the therapeutic bacterial strains must be attenuated or rendered sufficiently non-toxic so as to not cause systemic disease and/or septic shock, but still maintain some level of infectivity to effectively colonize tumors. Genetically modified bacteria have been described that are to be used as antitumor agents to elicit direct tumoricidal effects and/or to deliver tumoricidal molecules (Clairmont et al. (2000) J. Infect. Dis. 181:1996-2002; Bermudes, D. et al. (2002) Curr. Opin. Drug Discov. Devel. 5:194-199; Zhao, M. et al. (2005) Proc. Natl. Acad. Sci. USA 102:755-760; Zhao, M. et al. (2006) Cancer Res. 66:7647-7652). Among these are bioengineered strains of Salmonella enterica serovar Typhimurium (S. typhimurium). These bacteria accumulate preferentially >1,000-fold greater in tumors than in normal tissues and disperse homogeneously in tumor tissues (Pawelek, J. et al. (1997) Cancer Res. 57:4537-4544; Low, K. B. et al. (1999) Nat. Biotechnol. 17:37-41). Preferential replication allows the bacteria to produce and deliver a variety of anticancer therapeutic agents at high concentrations directly within the tumor, while minimizing toxicity to normal tissues. These attenuated bacteria are safe in mice, pigs, and monkeys when administered intravenously (Zhao, M. et al. (2005) Proc. Natl. Acad. Sci. USA 102:755-760; Zhao, M. et al. (2006) Cancer Res 66:7647-7652; Tjuvajev, J. et al. (2001) J. Control Release 74:313-315; Zheng, L. et al. (2000) Oncol. Res. 12:127-135), and certain live attenuated Salmonella strains have been shown to be well tolerated after oral administration in human clinical trials (Chatfield, S. N. et al. (1992) Bio/Technology 10:888-892; DiPetrillo, M. D. et al. (1999) Vaccine 18:449-459; Hohmann, E. L. et al. (1996) J. Infect. Dis. 173:1408-1414; Sirard, J. C. et al. (1999) Immunol. Rev. 171:5-26). The S. typhimurium phoP/phoQ operon is a typical bacterial two-component regulatory system composed of a membrane-associated sensor kinase (PhoQ) and a cytoplasmic transcriptional regulator (PhoP: Miller, S. I. et al. (1989) Proc. Natl. Acad. Sci. USA 86:5054-5058; Groisman, E. A. et al. (1989) Proc. Natl. Acad. Sci. USA 86: 7077-7081). PhoP/phoQ is required for virulence, and its deletion results in poor survival of this bacterium in macrophages and a marked attenuation in mice and humans (Miller, S. I. et al. (1989) Proc. Natl. Acad. Sci. USA 86:5054-5058; Groisman, E. A. et al. (1989) Proc. Natl. Acad. Sci. USA 86: 7077-7081; Galan, J. E. and Curtiss, R. III. (1989) Microb. Pathog. 6:433-443; Fields, P. I. et al. (1986) Proc. Natl. Acad. Sci. USA 83:5189-5193). PhoP/phoQ deletion strains have been employed as effective vaccine delivery vehicles (Galan, J. E. and Curtiss, R. III. (1989) Microb. Pathog. 6:433-443; Fields, P. I. et al. (1986) Proc. Natl. Acad. Sci. USA 83:5189-5193; Angelakopoulos, H. and Hohmann, E. L. (2000) Infect Immun. 68:2135-2141). Attenuated Salmonellae have been used for targeted delivery of tumoricidal proteins (Bermudes, D. et al. (2002) Curr. Opin. Drug Discov. Devel. 5:194-199; Tjuvajev J. et al. (2001) J. Control Release 74:313-315).

Bacterially-based cancer therapies have demonstrated limited clinical benefit. A variety of bacterial species, including Clostridium novyi (Dang et al. (2001) Proc. Natl. Acad. Sci. U.S.A. 98(26):15155-15160; U.S. Patent Publications Nos. 2017/0020931, 2015/0147315; U.S. Pat. Nos. 7,344,710; 3,936,354), Mycobacterium bovis (U.S. Patent Publication Nos. 2015/0224151, 2015/0071873), Bifidobacterium bifidum (Kimura et al. (1980) Cancer Res. 40:2061-2068), Lactobacillus casei (Yasutake et al. (1984) Med. Microbiol. Immunol. 173(3):113-125), Listeria monocytogenes (Le et al. (2012) Clin. Cancer Res. 18(3):858-868; Starks et al. (2004) J. Immunol. 173:420-427; U.S. Patent Publication No. 2006/0051380) and Escherichia coli (U.S. Pat. No. 9,320,787) have been studied as possible agents for anticancer therapy.

The Bacillus Calmette-Guerin (BCG) strain, for example, is approved for the treatment of bladder cancer in humans, and is more effective than intravesical chemotherapy, often being used as a first-line treatment (Gardlik et al. (2011) Gene therapy 18:425-431). Another approach utilizes Listeria monocytogenes, a live attenuated intracellular bacterium capable of inducing potent CD8⁺ T cell priming to expressed tumor antigens in mice (Le et al. (2012) Clin. Cancer Res. 18(3):858-868). In a clinical trial of the Listeria-based vaccine incorporating the tumor antigen mesothelin, together with an allogeneic pancreatic cancer-based GVAX vaccine in a prime-boost approach, a median survival of 6.1 months was noted in patients with advanced pancreatic cancer, versus a median survival of 3.9 months for patients treated with the GVAX vaccine alone (Le et al. (2015) J. Clin. Oncol. 33(12):1325-1333). These results were not replicated in a larger phase 2b study, possibly pointing to the difficulties in attempting to induce immunity to a low affinity self-antigen such as mesothelin.

Bacterial strains can be modified as described and exemplified herein to express inhibitory RNA (RNAi), such as shRNAs and microRNAs, that inhibit or disrupt TREX1 and/or PD-L1 and optionally one or more additional immune checkpoint genes. The strains can be attenuated by standard methods and/or by deletion or modification of genes, and by alteration or introduction of genes that render the bacteria able to grow in vivo primarily in immunoprivilaged environments, such as the TME, in tumor cells and solid tumors. Strains for modification as described herein can be selected from among, for example, Shigella, Listeria, E. coli, Bifidobacteriae and Salmonella. For example, Shigella sonnei, Shigella flexneri, Shigella dysenteriae, Listeria monocytogenes, Salmonella typhi, Salmonella typhimurium, Salmonella gallinarum, and Salmonella enteritidis. Other suitable bacterial species include Rickettsia, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Vibrio, Bacillus, and Erysipelothrix. For example, Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia tsutsugamuchi, Rickettsia mooseri, Rickettsia sibirica, Bordetella bronchiseptica, Neisseria meningitidis, Neisseria gonorrhoeae, Aeromonas eucrenophila, Aeromonas salmonicida, Francisella tularensis, Corynebacterium pseudotuberculosis, Citrobacter freundii, Chlamydia pneumoniae, Haemophilus somnus, Brucella abortus, Mycobacterium intracellulare, Legionella pneumophila, Rhodococcus equi, Pseudomonas aeruginosa, Helicobacter mustelae, Vibrio cholerae, Bacillus subtilis, Erysipelothrix rhusiopathiae, Yersinia enterocolitica, Rochalimaea quintana, and Agrobacterium tumerfacium. Any known therapeutic, including immunostimulatory, bacteria can be modified as described herein.

2. Comparison of the Immune Responses to Bacteria and Viruses

Bacteria, like viruses, have the advantage of being naturally immunostimulatory. Bacteria and viruses are known to contain conserved structures known as Pathogen-Associated Molecular Patterns (PAMPs), which are sensed by host cell Pattern Recognition Receptors (PRRs). Recognition of PAMPs by PRRs triggers downstream signaling cascades that result in the induction of cytokines and chemokines, and initiation of immune responses that lead to pathogen clearance (Iwasaki and Medzhitov (2010) Science 327(5963):291-295). The manner in which the innate immune system is engaged by PAMPs, and from what type of infectious agent, determines the appropriate adaptive immune response to combat the invading pathogen.

A class of PRRs known as Toll Like Receptors (TLRs) recognize PAMPs derived from bacterial and viral origins, and are located in various compartments within the cell. TLRs bind a range of ligands, including lipopolysaccharide (TLR4), lipoproteins (TLR2), flagellin (TLR5), unmethylated CpG motifs in DNA (TLR9), double-stranded RNA (TLR3), and single-stranded RNA (TLR7 and TLR8) (Akira et al. (2001) Nat. Immunol. 2(8):675-680; Kawai and Akira (2005) Curr. Opin. Immunol. 17(4):338-344). Host surveillance of S. typhimurium for example, is largely mediated through TLR2, TLR4 and TLR5 (Arpaia et al. (2011) Cell 144(5):675-688). These TLRs signal through MyD88 and TRIF adaptor molecules to mediate induction of NF-kB dependent pro-inflammatory cytokines such as TNF-α, IL-6 and IFN-γ (Pandey et al. (2015) Cold Spring Harb. Perspect. Biol. 7(1):a016246).

Another category of PRRs are the nod-like receptor (NLR) family. These receptors reside in the cytosol of host cells and recognize intracellular PAMPS. For example, S. typhimurium flagellin was shown to activate the NLRC4/NAIP5 inflammasome pathway, resulting in the cleavage of caspase-1 and induction of the pro-inflammatory cytokines IL-1β and IL-18, leading to pyroptotic cell death of infected macrophages (Fink et al. (2007) Cell Microbiol. 9(11):2562-2570).

While engagement of TLR2, TLR4, TLR5 and the inflammasome induces pro-inflammatory cytokines that mediate bacterial clearance, they activate a predominantly NF-κB-driven signaling cascade that leads to recruitment and activation of neutrophils, macrophages and CD4⁺ T cells, but not the DCs and CD8⁺ T cells that are required for anti-tumor immunity (Liu et al. (2017) Signal Transduct. Target Ther. 2:e17023). In order to activate CD8⁺ T cell-mediated anti-tumor immunity, IRF3/IRF7-dependent type I interferon signaling is critical for DC activation and cross-presentation of tumor antigens to promote CD8⁺ T cell priming (Diamond et al. (2011) J. Exp. Med. 208(10):1989-2003; Fuertes et al. (2011) J. Exp. Med. 208(10):2005-2016). Type I interferons (IFN-α, IFN-β) are the signature cytokines induced by two distinct TLR-dependent and TLR-independent signaling pathways. The TLR-dependent pathway for inducing IFN-β occurs following endocytosis of pathogens, whereby TLR3, 7, 8 and 9 detect pathogen-derived DNA and RNA elements within the endosomes. TLRs 7 and 8 recognize viral nucleosides and nucleotides, and synthetic agonists of these, such as resiquimod and imiquimod have been clinically validated (Chi et al. (2017) Frontiers in Pharmacology 8:304). Synthetic dsRNA, such as polyinosinic:polycytidylic acid (poly (I:C)) and poly ICLC, an analog that is formulated with poly L lysine to resist RNase digestion, is an agonist for TLR3 and MDA5 pathways and a powerful inducer of IFN-β (Caskey et al. (2011) J. Exp. Med. 208(12):2357-66). TLR9 detection of endosomal CpG motifs present in viral and bacterial DNA can also induce IFN-β via IRF3. Additionally, TLR4 has been shown to induce IFN-β via MyD88-independent TRIF activation of IRF3 (Owen et al. (2016) mBio. 7(1):e02051-15). It subsequently was shown that TLR4 activation of DCs was independent of type I IFN, so the ability of TLR4 to activate DCs via type I IFN is not likely biologically relevant (Hu et al. (2015) Proc. Natl. Acad. Sci. U.S.A. 112(45):13994-13999). Further, TLR4 signaling has not been shown to directly recruit or activate CD8⁺ T cells.

Of the TLR-independent type I IFN pathways, one is mediated by host recognition of single-stranded (ss) and double-stranded (ds) RNA in the cytosol. These are sensed by RNA helicases, including retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA-5), and through the IFN-β promoter stimulator 1 (IPS-1; also known as mitochondrial antiviral-signaling protein or MAVS) adaptor protein-mediated phosphorylation of the IRF-3 transcription factor, leading to induction of IFN-β (Ireton and Gale (2011) Viruses 3(6):906-919). Synthetic RIG-I-binding elements have also been discovered unintentionally in common lentiviral shRNA vectors, in the form of an AA dinucleotide sequence at the U6 promoter transcription start site. Its subsequent deletion in the plasmid prevented confounding off-target type I IFN activation (Pebernard et al. (2004) Differentiation 72:103-111).

The second type of TLR-independent type I interferon induction pathway is mediated through Stimulator of Interferon Genes (STING), a cytosolic ER-resident adaptor protein that is now recognized as the central mediator for sensing cytosolic dsDNA from infectious pathogens or aberrant host cell damage (Barber (2011) Immunol. Rev. 243(1):99-108). STING signaling activates the TANK binding kinase (TBK1)/IRF3 axis and the NF-kB signaling axis, resulting in the induction of IFN-β and other pro-inflammatory cytokines and chemokines that strongly activate innate and adaptive immunity (Burdette et al. (2011) Nature 478(7370):515-518). Sensing of cytosolic dsDNA through STING requires cyclic GMP-AMP synthase (cGAS), a host cell nucleotidyl transferase that directly binds dsDNA, and in response, synthesizes a cyclic dinucleotide (CDN) second messenger, cyclic GMP-AMP (cGAMP), which binds and activates STING (Sun et al. (2013) Science 339(6121):786-791; Wu et al. (2013) Science 339(6121):826-830). CDNs derived from bacteria such as c-di-AMP produced from intracellular Listeria monocytogenes can also directly bind murine STING, but only 3 of the 5 human STING alleles. Unlike the CDNs produced by bacteria, in which the two purine nucleosides are joined by a phosphate bridge with 3′-3′ linkages, the internucleotide phosphate bridge in the cGAMP synthesized by mammalian cGAS is joined by a non-canonical 2′-3′ linkage. These 2′-3′ molecules bind to STING with 300-fold better affinity than bacterial 3′-3′ CDNs, and thus are more potent physiological ligands of human STING (see, e.g., Civril et al. (2013) Nature 498(7454):332-337; Diner et al. (2013) Cell Rep. 3(5):1355-1361; Gao et al. (2013) Sci. Signal 6(269):pl1; Ablasser et al. (2013) Nature 503(7477):530-534).

The cGAS/STING signaling pathway in humans may have evolved over time to preferentially respond to viral pathogens over bacterial pathogens, and this can explain why bacterial vaccines harboring host tumor antigens have made for poor CD8⁺ T cell priming vectors in humans. TLR-independent activation of CD8⁺ T cells by STING-dependent type I IFN signaling from conventional DCs is the primary mechanism by which viruses are detected, with TLR-dependent type I IFN production by plasmacytoid DCs operating only when the STING pathway has been virally-inactivated (Hervas-Stubbs et al. (2014) J. Immunol. 193:1151-1161). Further, for bacteria such as S. typhimurium, while capable of inducing IFN-3 via TLR4, CD8⁺ T cells are neither induced nor required for clearance or protective immunity (Lee et al. (2012) Immunol. Lett. 148(2): 138-143). The lack of physiologically relevant CD8⁺ T epitopes for many strains of bacteria, including S. typhimurium, has impeded both bacterial vaccine development and protective immunity to subsequent infections, even from the same genetic strains (Lo et al. (1999) J. Immunol. 162:5398-5406). Thus, bacterially-based cancer immunotherapies are biologically limited in their ability to induce type I IFN to recruit and activate CD8⁺ T cells, necessary to promote tumor antigen cross-presentation and durable anti-tumor immunity. Hence, engineering a bacterial immunotherapy provided herein to induce viral-like TLR-independent type I IFN signaling, rather than TLR-dependent bacterial immune signaling, will preferentially induce CD8⁺ T cell mediated anti-tumor immunity.

STING activates innate immunity in response to sensing nucleic acids in the cytosol. Downstream signaling is activated through binding of CDNs, which are synthesized by bacteria or by the host enzyme cGAS in response to binding to cytosolic dsDNA. Bacterial and host-produced CDNs have distinct phosphate bridge structures, which differentiates their capacity to activate STING. IFN-3 is the signature cytokine of activated STING, and virally-induce type I IFN, rather than bacterially-induced IFN, is required for effective CD8⁺ T cell mediated anti-tumor immunity. Immunostimulatory bacteria provided herein include those that are STING agonists.

3. Salmonella Therapy

Salmonella is exemplary of a bacterial genus that can be used as a cancer therapeutic. The Salmonella exemplified herein is an attenuated species or one that, by virtue of the modifications for use as a cancer therapeutic, has reduced toxicity.

a. Tumor-Tropic Bacteria

A number of bacterial species have demonstrated preferential replication within solid tumors when injected from a distal site. These include, but are not limited to, species of Salmonella, Bifodobacterium, Clostridium, and Escherichia. The natural tumor-homing properties of the bacteria combined with the host's innate immune response to the bacterial infection is thought to mediate the anti-tumor response. This tumor tissue tropism has been shown to reduce the size of tumors to varying degrees. One contributing factor to the tumor tropism of these bacterial species is the ability to replicate in anoxic or hypoxic environments. A number of these naturally tumor-tropic bacteria have been further engineered to increase the potency of the antitumor response (reviewed in Zu et al. (2014) Crit. Rev. Microbiol. 40(3):225-235; and Felgner et al. (2017) Microbial Biotechnology 10(5):1074-1078).

b. Salmonella enterica Serovar typhimurium

Salmonella enterica Serovar Typhimurium (S. typhimurium) is exemplary of a bacterial species for use as an anti-cancer therapeutic. One approach to using bacteria to stimulate host immunity to cancer has been through the Gram-negative facultative anaerobe S. typhimurium, which preferentially accumulates in hypoxic and necrotic areas in the body, including tumor microenvironments. S. typhimurium accumulates in these environments due to the availability of nutrients from tissue necrosis, the leaky tumor vasculature and their increased likelihood to survive in the immune system-evading tumor microenvironment (Baban et al. (2010) Bioengineered Bugs 1(6):385-394). S. typhimurium is able to grow under both aerobic and anaerobic conditions; therefore it is able to colonize small tumors that are less hypoxic and large tumors that are more hypoxic.

S. typhimurium is a Gram-negative, facultative pathogen that is transmitted via the fecal-oral route. It causes localized gastrointestinal infections, but also enters the bloodstream and lymphatic system after oral ingestion, infecting systemic tissues such as the liver, spleen and lungs. Systemic administration of wild-type S. typhimurium overstimulates TNF-α induction, leading to a cytokine cascade and septic shock, which, if left untreated, can be fatal. As a result, pathogenic bacterial strains, such as S. typhimurium, must be attenuated to prevent systemic infection, without completely suppressing their ability to effectively colonize tumor tissues. Attenuation is often achieved by mutating a cellular structure that can elicit an immune response, such as the bacterial outer membrane or limiting its ability to replicate in the absence of supplemental nutrients.

S. typhimurium is an intracellular pathogen that is rapidly taken up by myeloid cells such as macrophages or it can induce its own uptake in in non-phagocytic cells such as epithelial cells. Once inside cells, it can replicate within a Salmonella containing vacuole (SCV) and can also escape into the cytosol of some epithelial cells. Many of the molecular determinants of S. typhimurium pathogenicity have been identified and the genes are clustered in Salmonella pathogenicity islands (SPIs). The two best characterized pathogenicity islands are SPI-1 which is responsible for mediating bacterial invasion of non-phagocytic cells, and SPI-2 which is required for replication within the SCV (Agbor and McCormick (2011) Cell Microbiol. 13(12): 1858-1869). Both of these pathogenicity islands encode macromolecular structures called type three secretion systems (T3SS) that can translocate effector proteins across the host membrane (Galan and Wolf-Watz (2006) Nature 444:567-573).

c. Bacterial Attenuation

Therapeutic bacteria for administration as a cancer treatment should be attenuated. Various methods for attenuation of bacterial pathogens are known in the art. Auxotrophic mutations, for example, render bacteria incapable of synthesizing an essential nutrient, and deletions/mutations in genes such as aro, pur, gua, thy, nad and asd (U.S. Patent Publication No. 2012/0009153) are widely used. Nutrients produced by the biosynthesis pathways involving these genes are often unavailable in host cells, and as such, bacterial survival is challenging. For example, attenuation of Salmonella and other species can be achieved by deletion of the aroA gene, which is part of the shikimate pathway, connecting glycolysis to aromatic amino acid biosynthesis (Felgner et al. (2016) MBio 7(5):e01220-16). Deletion of aroA therefore results in bacterial auxotrophy for aromatic amino acids and subsequent attenuation (U.S. Patent Publication Nos. 2003/0170276, 2003/0175297, 2012/0009153, 2016/0369282; International Application Publication Nos. WO 2015/032165 and WO 2016/025582). Similarly, other enzymes involved in the biosynthesis pathway for aromatic amino acids, including aroC and aroD have been deleted to achieve attenuation (U.S. Patent Publication No. 2016/0369282; International Patent Application Publication No. WO 2016/025582). For example, S. typhimurium strain SL7207 is an aromatic amino acid auxotroph (aroA mutant); strains A1 and A1-R are leucine-arginine auxotrophs. VNP20009 is a purine auxotroph (purI⁻ mutant). As shown herein, it is also auxotrophic for the immunosuppressive nucleoside adenosine.

Mutations that attenuate bacteria also include, but are not limited to, mutations in genes that alter the biosynthesis of lipopolysaccharide, such as rfaL, rfaG, rfaH, rfaD, rfaP, rFb, rfa, msbB, htrB, firA, pagL, pagP, lpxR, arnT, eptA, and lpxT; mutations that introduce a suicide gene such as sacB, nuk, hok, gef, kil or phlA; mutations that introduce a bacterial lysis gene such as hly and cly; mutations in virulence factors such as IsyA, pag, prg, iscA, virG, plc and act; mutations that modify the stress response such as recA, htrA, htpR, hsp and groEL; mutations that disrupt the cell cycle such as min; and mutations that disrupt or inactivate regulatory functions, such as cya, crp, phoP/phoQ, and ompR (U.S. Patent Publication Nos. 2012/0009153, 2003/0170276, 2007/0298012; U.S. Pat. No. 6,190,657; International Application Publication No. WO 2015/032165; Felgner et al. (2016) Gut microbes 7(2):171-177; Broadway et al. (2014) J. Biotechnology 192:177-178; Frahm et al. (2015) mBio 6(2):e00254-15; Kong et al. (2011) Infection and Immunity 79(12):5027-5038; Kong et al. (2012) Proc. Natl. Acad. Sci. USA 109(47): 19414-19419). Ideally, the genetic attenuations comprise gene deletions rather than point mutations to prevent spontaneous compensatory mutations that might result in reversion to a virulent phenotype.

i. msbB⁻ Mutants

The enzyme lipid A biosynthesis myristoyltransferase, encoded by the msbB gene in S. typhimurium, catalyzes the addition of a terminal myristyl group to the lipid A domain of lipopolysaccharide (LPS) (Low et al. (1999) Nat. Biotechnol. 17(1):37-41). Deletion of msbB thus alters the acyl composition of the lipid A domain of LPS, the major component of the outer membranes of Gram-negative bacteria. This modification significantly reduces the ability of the LPS to induce septic shock, attenuating the bacterial strain and reducing the potentially harmful production of TNFα, thus lowering systemic toxicity. S. typhimurium msbB mutants maintain their ability to preferentially colonize tumors over other tissues in mice and retain anti-tumor activity, thus increasing the therapeutic index of Salmonella based immunotherapeutics (U.S. Patent Publication Nos. 2003/0170276, 2003/0109026, 2004/0229338, 2005/02250882005/0255088, 2007/0298012).

For example, deletion of msbB in the S. typhimurium strain VNP20009 results in production of a predominantly penta-acylated LPS, which is less toxic than native hexa-acylated LPS and allows for systemic delivery without the induction of toxic shock (Lee et al. (2000) International Journal of Toxicology 19:19-25). Other LPS mutations can be introduced into the bacterial strains provided herein, including the Salmonella strains, that dramatically reduce virulence, and thereby provide for lower toxicity, and permit administration of higher doses.

ii. purI⁻ Mutants

Immunostimulatory bacteria that can be attenuated by rendering them auxotrophic for one or more essential nutrients, such as purines (for example, adenine), nucleosides (for example, adenosine) or amino acids (for example, arginine and leucine), are employed. In particular, in embodiments of the immunostimulatory bacteria provided herein, such as S. typhimurium, the bacteria are rendered auxotrophic for adenosine, which preferentially accumulates in tumor microenvironments. Hence, strains of immunostimulatory bacteria described herein are attenuated because they require adenosine for growth, and they preferentially colonize TMEs, which, as discussed below, have an abundance of adenosine.

Phosphoribosylaminoimidazole synthetase, an enzyme encoded by the purI gene (synonymous with the purM gene), is involved in the biosynthesis pathway of purines. Disruption of the purI gene thus renders the bacteria auxotrophic for purines. In addition to being attenuated, purI⁻ mutants are enriched in the tumor environment and have significant anti-tumor activity (Pawelek et al. (1997) Cancer Research 57:4537-4544). It was previously described that this colonization results from the high concentration of purines present in the interstitial fluid of tumors as a result of their rapid cellular turnover. Since the purI bacteria are unable to synthesize purines, they require an external source of adenine, and it was thought that this would lead to their restricted growth in the purine-enriched tumor microenvironment (Rosenberg et al. (2002) J. Immunotherapy 25(3):218-225). While the VNP20009 strain was initially reported to contain a deletion of the purI⁻ gene (Low et al. (2003) Methods in Molecular Medicine Vol. 90, Suicide Gene Therapy: 47-59), subsequent analysis of the entire genome of VNP20009 demonstrated that the purI⁻ gene is not deleted, but is disrupted by a chromosomal inversion (Broadway et al. (2014) Journal of Biotechnology 192:177-178). The entire gene is contained within two parts of the VNP20009 chromosome that is flanked by insertion sequences (one of which has an active transposase).

It is shown herein, that, purI mutant S. typhimurium strains are auxotrophic for the nucleoside adenosine, which is highly enriched in tumor microenvironments. Hence, when using VNP20009, it is not necessary to introduce any further modification to achieve adenosine auxotrophy. For other strains and bacteria, the purI gene can be disrupted as it has been in VNP20009, or it can contain a deletion of all or a portion of the purI gene to prevent reversion to a wild-type gene.

iii. Combinations of Attenuating Mutations

A bacterium with multiple genetic attenuations by means of gene deletions on disparate regions of the chromosome is desirable for bacterial immunotherapies because the attenuation can be increased, while decreasing the possibility of reversion to a virulent phenotype by acquisition of genes by homologous recombination with a wild-type genetic material. Restoration of virulence by homologous recombination would require two separate recombination events to occur within the same organism. Ideally the combinations of attenuating mutations selected for use in an immunotherapeutic agent increases the tolerability without decreasing the potency, thereby increasing the therapeutic index. For example, disruption of the msbB and purI genes in S. typhimurium strain VNP20009, has been used for tumor-targeting and growth suppression, and elicits low toxicity in animal models (Clairmont et al. (2000) J. Infect. Dis. 181:1996-2002; Bermudes et al. (2000) Cancer Gene Therapy: Past Achievements and Future Challenges, edited by Habib Kluwer Academic/Plenum Publishers, New York, pp. 57-63; Low et al. (2003) Methods in Molecular Medicine, Vol. 90, Suicide Gene Therapy: 47-59; Lee et al. (2000) International Journal of Toxicology 19:19-25; Rosenberg et al. (2002) J. Immunotherapy 25(3):218-225; Broadway et al. (2014) J. Biotechnology 192:177-178; Loeffler et al. (2007) Proc. Natl. Acad. Sci. U.S.A. 104(31):12879-12883; Luo et al. (2002) Oncology Research 12:501-508). When VNP20009 (msbB⁻/purI⁻) was administered to mice bearing syngeneic or human xenograft tumors, the bacteria accumulated preferentially within the extracellular components of tumors at ratios exceeding 300-1000 to 1, reduced TNFα induction, and demonstrated tumor regression and prolonged survival compared to control mice (Clairmont et al. (2000) J. Infect. Dis. 181:1996-2002). Results from the Phase 1 clinical trial in humans, however, revealed that while VNP20009 was relatively safe and well tolerated, poor accumulation was observed in human melanoma tumors, and very little anti-tumor activity was demonstrated (Toso et al. (2002) J. Clin. Oncol. 20(1): 142-152). Higher doses, which are required to manifest any anti-tumor activity, were not possible due to toxicity.

Thus, further improvements are needed. The immunostimulatory bacteria provided herein address this problem.

iv. VNP20009 and Other Attenuated and Wild-Type S. typhimurium Strains

The starting strain can be a wild-type non-attenuated strain, such as a strain having all of the identifying characteristics of ATCC 14028. The strain is then modified to increase its specificity or targeting to the tumor microenvironment or to tumor cells and/or to tumor resident immune cells. It also can be modified to be auxotrophic for adenosine. The strain can be rendered flagellin⁻ (fliC⁻/fljB⁻), and optionally one or more of msbB⁻, purI⁻/M⁻, and pagP⁻. The strains also can be asd⁻. The modified strains encode a therapeutic product on a plasmid, generally present in low to medium copy number, under control of a promoter recognized by a mammalian host, such as RNA polymerase II or III. Additional regulatory sequences to control expression in the tumor microenvironment and trafficking in the cells also can be included.

Exemplary of a therapeutic bacterium that can be modified as described herein is the strain designated as VNP20009 (ATCC #202165, YS1646), which is derived from the strain ATCC accession no. 14028. The strain designated VNP20009 (ATCC #202165, YS1646), was a clinical candidate, and at least 50,000-fold attenuated for safety by deletion of the msbB and purI⁻ genes (Clairmont et al. (2000) J. Infect. Dis. 181:1996-2002; Low et al. (2003) Methods in Molecular Medicine, Vol. 90, Suicide Gene Therapy: 47-59; Lee et al. (2000) International Journal of Toxicology 19:19-25). Similar strains of Salmonella that are attenuated also are contemplated. As described above, deletion of msbB alters the composition of the lipid A domain of lipopolysaccharide, the major component of Gram-negative bacterial outer membranes (Low et al. (1999) Nat. Biotechnol. 17(1):37-41). This prevents lipopolysaccharide-induced septic shock, attenuating the bacterial strain and lowering systemic toxicity, while reducing the potentially harmful production of TNFα (Dinarello, C. A. (1997) Chest 112(6 Suppl):321S-329S; Low et al. (1999) Nat. Biotechnol. 17(1):37-41). Deletion of the purI⁻ gene renders the bacteria auxotrophic for purines, which further attenuates the bacteria and enriches it in the tumor microenvironment (Pawelek et al. (1997) Cancer Res. 57:4537-4544; Broadway et al. (2014) J. Biotechnology 192:177-178).

Accumulation of VNP20009 in tumors results from a combination of factors including: the inherent invasiveness of the parental strain, ATCC accession number 14028, its ability to replicate in hypoxic environments, and its requirement for high concentrations of purines that are present in the interstitial fluid of tumors. It is shown herein that VNP20009 also is auxotrophic for the nucleoside adenosine, which can accumulate to pathologically high levels in the tumor microenvironment and contribute to an immunosuppressive tumor microenvironment (Peter Vaupel and Arnulf Mayer Oxygen Transport to Tissue XXXVII, Advances in Experimental Medicine and Biology 876 chapter 22, pp. 177-183). VNP20009 was administered into mice bearing syngeneic or human xenograft tumors, the bacteria accumulated preferentially within the extracellular components of tumors at ratios exceeding 300-1000 to 1 and demonstrated tumor growth inhibition as well as prolonged survival compared to control mice (Clairmont et al. (2000) J. Infect. Dis. 181:1996-2002). Results from the Phase 1 clinical trial revealed that while VNP20009 was relatively safe and well tolerated, poor accumulation was observed in human melanoma tumors, and very little anti-tumor activity was demonstrated (Toso et al. (2002) J. Clin. Oncol. 20(1):142-152). Higher doses, which would be required to affect any anti-tumor activity, were not possible due to toxicity that correlated with high levels of pro-inflammatory cytokines. The modifications provided herein, including the flagellin deletion (fliC⁻/fljB⁻), and optional pagP⁻ and/or hilA⁻ modifications, significantly increase accumulation of the immunostimulatory bacteria in tumors, in the tumor microenvironment and/or in tumor-resident immune cells, such as myeloid cells. Other modifications that increase targeting to immune cells, and eliminate infection of other cells, such as epithelial cells, increase the accumulation of the bacteria in the tumors and in the tumor microenvironment. Additional modifications to render the wild-type bacteria auxotrophic for adenosine further increases accumulation in the tumor microenvironment.

Other strains of S. typhimurium can be used for tumor-targeted delivery of therapeutic proteins and therapy, such as, for example, leucine-arginine auxotroph A-1 (Zhao et al. (2005) Proc. Natl. Acad. Sci. USA 102(3):755-760; Yu et al. (2012) Scientific Reports 2:436; U.S. Pat. No. 8,822,194; U.S. Patent Publication No. 2014/0178341) and its derivative AR-1 (Yu et al. (2012) Scientific Reports 2:436; Kawaguchi et al. (2017) Oncotarget 8(12):19065-19073; Zhao et al. (2006) Cancer Res. 66(15):7647-7652; Zhao et al. (2012) Cell Cycle 11(1):187-193; Tome et al. (2013) Anticancer Research 33:97-102; Murakami et al. (2017) Oncotarget 8(5):8035-8042; Liu et al. (2016) Oncotarget 7(16):22873-22882; Binder et al. (2013) Cancer Immunol Res. 1(2):123-133); aroA⁻ mutant S. typhimurium strain SL7207 (Guo et al. (2011) Gene therapy 18:95-105; U.S. Patent Publication Nos. 2012/0009153, 2016/0369282 and 2016/0184456) and its obligate anaerobe derivative YB1 (International Application Publication No. WO 2015/032165; Yu et al. (2012) Scientific Reports 2:436; Leschner et al. (2009) PLoS ONE 4(8): e6692; aroA⁻/aroD⁻ mutant S. typhimurium strain BRD509, a derivative of the SL1344 (WT) strain (Yoon et al. (2017) European J. of Cancer 70:48-61); asd⁻/cya⁻/crp⁻ mutant S. typhimurium strain χ4550 (Sorenson et al. (2010) Biologics: Targets & Therapy 4:61-73) and phoP⁻/phoQ⁻ S. typhimurium strain LH430 (International Application Publication No. WO 2008/091375).

The strain VNP20009 failed to show a clinical benefit in a study involving patients with advanced melanoma, but the treatment was safely administered to advanced cancer patients. A maximum tolerated dose (MTD) was established. Hence, this strain, as well as other similarly engineered bacterial strains, can be used as a starting material for tumor-targeting, therapeutic delivery vehicles. Modifications provided herein provide a strategy to increase efficacy, by increasing the anti-tumor efficiency and/or the safety and tolerability of the therapeutic agent.

v. S. typhimurium Engineered To Deliver Macromolecules

S. typhimurium also has been modified to deliver the tumor-associated antigen (TAA) survivin (SVN) to APCs to prime adaptive immunity (U.S. Patent Publication No. 2014/0186401; Xu et al. (2014) Cancer Res. 74(21):6260-6270). SVN is an inhibitor of apoptosis protein (IAP) which prolongs cell survival and provides cell cycle control, and is overexpressed in all solid tumors and poorly expressed in normal tissues. This technology utilizes Salmonella Pathogenicity Island 2 (SPI-2) and its type III secretion system (T3SS) to deliver the TAAs into the cytosol of APCs, which then are activated to induce TAA-specific CD8⁺ T cells and anti-tumor immunity (Xu et al. (2014) Cancer Res. 74(21):6260-6270). Similar to the Listeria-based TAA vaccines, this approach has shown promise in mouse models, but has yet to demonstrate effective tumor antigen-specific T cell priming in humans.

In addition to gene delivery, S. typhimurium also has been used for the delivery of small interfering RNAs (siRNAs) and short hairpin RNAs (shRNAs) for cancer therapy. For example, attenuated S. typhimurium have been modified to express certain shRNAs, such as those that target STAT3 and IDO1 (PCT/US2007/074272, and U.S. Pat. No. 9,453,227). VNP20009 transformed with an shRNA plasmid against the immunosuppressive gene indolamine deoxygenase (IDO), successfully silenced IDO expression in a murine melanoma model, resulting in tumor cell death and significant tumor infiltration by neutrophils (Blache et al. (2012) Cancer Res. 72(24):6447-6456). Combining this vector with the co-administration of a hyaluronidase, such as PEGylated soluble PH20 (PEGPH20; an enzyme that depletes extracellular hyaluronan), shows positive results in the treatment of pancreatic ductal adenocarcinoma tumors (Manuel et al. (2015) Cancer Immunol. Res. 3(9): 1096-1107; U.S. Patent Publication No. 2016/0184456). In another study, an S. typhimurium strain attenuated by a phoP/phoQ deletion and expressing a signal transducer and activator of transcription 3 (STAT3)-specific shRNA, was found to inhibit tumor growth and reduce the number of metastatic organs, extending the life of C57BL6 mice (Zhang et al. (2007) Cancer Res. 67(12):5859-5864). In another example, S. typhimurium strain SL7207 has been used for the delivery of shRNA targeting CTNNB1, the gene that encodes β-catenin (Guo et al. (2011) Gene therapy 18:95-105; U.S. Patent Publication Nos. 2009/0123426, 2016/0369282), while S. typhimurium strain VNP20009 has been used in the delivery of shRNA targeting the STAT3 (Manuel et al. (2011) Cancer Res. 71(12):4183-4191; U.S. Patent Publication Nos. 2009/0208534, 2014/0186401, 2016/0184456; International Application Publication Nos. WO 2008/091375, WO 2012/149364). siRNAs targeting the autophagy genes Atg5 and Beclin1 have been delivered to tumor cells using S. typhimurium strains A1-R and VNP20009 (Liu et al. (2016) Oncotarget 7(16):22873-22882). Improvement of such strains is needed so that they more effectively colonize tumors, the TME, and/or tumor-resident immune cells, and also stimulate the immune response, and have other advantageous properties, such as the immunostimulatory bacteria provided herein. Modifications of various bacteria have been described in International PCT Application Publication No. WO 2019/014398 and U.S. Publication No. 2019/0017050 A1. The bacteria described in each of these publications, also described herein, can be modified as described herein to further

The bacteria can be modified as described herein to have reduced inflammatory effects, and thus, to be less toxic. As a result, for example, higher dosages can be administered. Any of these strains of Salmonella, as well as other species of bacteria, known to those of skill in the art and/or listed above and herein, can be modified as described herein, such as by introducing adenosine auxotrophy, a plasmid encoding a therapeutic product, such as an immunostimulatory protein and/or RNAi, such as miRNA or shRNA, or an antibody or fragment thereof, for inhibiting an immune checkpoint, and other modifications as described herein. Exemplary are the S. typhimurium species described herein.

The bacterial strains provided herein are engineered to deliver therapeutic molecules. The strains herein deliver immunostimulatory proteins, such as cytokines, that promote an anti-tumor immune response in the tumor microenvironment. The strains also can include genomic modifications that reduce pyroptosis of phagocytic cells, thereby providing for a more robust immune response, and/or reduce or eliminate the ability to infect/invade epithelial cells, but retain the ability to infect/invade phagocytic cells, so that they accumulate more effectively in tumors and in tumor-resident immune cells. The bacterial strains also can be modified to encode therapeutic products, including, for example, RNAi targeted and inhibitory to immune checkpoints, and also to other such targets.

4. Enhancements of Immunostimulatory Bacteria to Increase Therapeutic Index

Provided herein are enhancements to immunostimulatory bacteria that reduce toxicity and improve the anti-tumor activity. Exemplary of such enhancements are the following. They are described with respect to Salmonella, particularly S. typhimurium; it is understood that the skilled person can effect similar enhancements in other bacterial species and other Salmonella strains.

a. asd Gene Deletion

The asd gene in bacteria encodes an aspartate-semialdehyde dehydrogenase. asd-mutants of S. typhimurium have an obligate requirement for diaminopimelic acid (DAP) which is required for cell wall synthesis and will undergo lysis in environments deprived of DAP. This DAP auxotrophy can be used for plasmid selection and maintenance of plasmid stability in vivo without the use of antibiotics when the asd gene is complemented in trans on a plasmid. Non-antibiotic-based plasmid selection systems are advantageous and allow for 1) use of administered antibiotics as rapid clearance mechanism in the event of adverse symptoms, and 2) for antibiotic-free scale up of production, where such use is commonly avoided. The asd gene complementation system provides for such selection (Galán et al. (1990) Gene 94(1):29-35). The use of the asd gene complementation system to maintain plasmids in the tumor microenvironment is expected to increase the potency of S. typhimurium engineered to deliver plasmids encoding genes or interfering RNAs.

An alternative use for an asd mutant of S. typhimurium is to exploit the DAP auxotrophy to produce an autolytic (or suicidal) strain for delivery of macromolecules to infected cells without the ability to persistently colonize host tumors. Deletion of the asd gene makes the bacteria auxotrophic for DAP when grown in vitro or in vivo. An example described herein, provides an asd deletion strain that is auxotrophic for DAP and contains a plasmid suitable for delivery of RNAi, such as shRNA or mi-RNA, that does not contain an asd complementing gene, resulting in a strain that is defective for replication in vivo. This strain is propagated in vitro in the presence of DAP and grows normally, and then is administered as an immunotherapeutic agent to a mammalian host where DAP is not present. The suicidal strain is able to invade host cells but is not be able to replicate due to the absence of DAP in mammalian tissues, lysing automatically and delivering its cytosolic contents (e.g., plasmids or proteins). In examples provided herein, an asd gene deleted strain of VNP20009 was further modified to express an LLO protein lacking its endogenous periplasmic secretion signal sequence, causing it to accumulate in the cytoplasm of the Salmonella. LLO is a cholesterol-dependent pore forming hemolysin from Listeria monocytogenes that mediates phagosomal escape of bacteria. When the autolytic strain is introduced into tumor bearing mice, the bacteria are taken up by phagocytic immune cells and enter the Salmonella containing vacuole (SCV). In this environment, the lack of DAP will prevent bacterial replication, and result in autolysis of the bacteria in the SCV. Lysis of the suicidal strain will then allow for release of the plasmid and the accumulated LLO that will form pores in the cholesterol-containing SVC membrane, and allow for delivery of the plasmid into the cytosol of the host cell.

b. Adenosine Auxotrophy

Metabolites derived from the tryptophan and ATP/adenosine pathways are major drivers in forming an immunosuppressive environment within the tumor. Adenosine, which exists in the free form inside and outside of cells, is an effector of immune function. Adenosine decreases T-cell receptor induced activation of NF-κB, and inhibits IL-2, IL-4, and IFN-γ. Adenosine decreases T-cell cytotoxicity, increases T-cell anergy, and increases T-cell differentiation to Foxp3⁺ or Lag-3⁺ regulatory (T-reg) T-cells. On NK cells, adenosine decreases IFN-γ production, and suppresses NK cell cytotoxicity. Adenosine blocks neutrophil adhesion and extravasation, decreases phagocytosis, and attenuates levels of superoxide and nitric oxide. Adenosine also decreases the expression of TNF-α, IL-12, and MIP-1α on macrophages, attenuates MHC Class II expression, and increases levels of IL-10 and IL-6. Adenosine immunomodulation activity occurs after its release into the extracellular space of the tumor and activation of adenosine receptors (ADRs) on the surface of target immune cells, cancer cells or endothelial cells. The high adenosine levels in the tumor microenvironment result in local immunosuppression, which limits the capacity of the immune system to eliminate cancer cells.

Extracellular adenosine is produced by the sequential activities of membrane associated ectoenzymes, CD39 and CD73, which are expressed on tumor stromal cells, together producing adenosine by phosphohydrolysis of ATP or ADP produced from dead or dying cells. CD39 converts extracellular ATP (or ADP) to 5′AMP, which is converted to adenosine by 5′AMP. Expression of CD39 and CD73 on endothelial cells is increased under the hypoxic conditions of the tumor microenvironment, thereby increasing levels of adenosine. Tumor hypoxia can result from inadequate blood supply and disorganized tumor vasculature, impairing delivery of oxygen (Carroll and Ashcroft (2005) Expert. Rev. Mol. Med. 7(6): 1-16). Hypoxia, which occurs in the tumor microenvironment, also inhibits adenylate kinase (AK), which converts adenosine to AMP, leading to very high extracellular adenosine concentrations. The extracellular concentration of adenosine in the hypoxic tumor microenvironment has been measured at 10-100 μM, which is up to about 100-1000 fold higher than the typical extracellular adenosine concentration of approximately 0.1 μM (Vaupel et al. (2016) Adv. Exp. Med. Biol. 876:177-183; Antonioli et al. (2013) Nat. Rev. Can. 13:842-857). Since hypoxic regions in tumors are distal from microvessels, the local concentration of adenosine in some regions of the tumor can be higher than others.

To direct effects to inhibit the immune system, adenosine also can control cancer cell growth and dissemination by effects on cancer cell proliferation, apoptosis and angiogenesis. For example, adenosine can promote angiogenesis, primarily through the stimulation of A_(2A) and A_(2B) receptors. Stimulation of the receptors on endothelial cells can regulate the expression of intercellular adhesion molecule 1 (ICAM-1) and E-selectin on endothelial cells, maintain vascular integrity, and promote vessel growth (Antonioli et al. (2013) Nat. Rev. Can. 13:842-857). Activation of one or more of A_(2A), A_(2B) or A₃ on various cells by adenosine can stimulate the production of the pro-angiogenic factors, such as vascular endothelial growth factor (VEGF), interleukin-8 (IL-8) or angiopoietin 2 (Antonioli et al. (2013) Nat. Rev. Can. 13:842-857).

Adenosine also can directly regulate tumor cell proliferation, apoptosis and metastasis through interaction with receptors on cancer cells. For example, studies have shown that the activation of A₁ and A_(2A) receptors promote tumor cell proliferation in some breast cancer cell lines, and activation of A_(2B) receptors have cancer growth-promoting properties in colon carcinoma cells (Antonioli et al. (2013) Nat. Rev. Can. 13:842-857). Adenosine also can trigger apoptosis of cancer cells, and various studies have correlated this activity to activation of the extrinsic apoptotic pathway through A₃ or the intrinsic apoptotic pathway through A_(2A) and A_(2B) (Antonioli et al. (2013)). Adenosine can promote tumor cell migration and metastasis, by increasing cell motility, adhesion to the extracellular matrix, and expression of cell attachment proteins and receptors to promote cell movement and motility.

The extracellular release of adenosine triphosphate (ATP) occurs from stimulated immune cells and damaged, dying or stressed cells. The NLR family pyrin domain-containing 3 (NLRP3) inflammasome, when stimulated by this extracellular release of ATP, activates caspase-1 and results in the secretion of the cytokines IL-1β and IL-18, which in turn activate innate and adaptive immune responses (Stagg and Smyth (2010) Oncogene 29:5346-5358). ATP is catabolized into adenosine by the enzymes CD39 and CD73. Activated adenosine acts as a highly immunosuppressive metabolite via a negative-feedback mechanism and has a pleiotropic effect against multiple immune cell types in the hypoxic tumor microenvironment (Stagg and Smyth (2010) Oncogene 29:5346-5358). Adenosine receptors A_(2A) and A_(2B) are expressed on a variety of immune cells and are stimulated by adenosine to promote cAMP-mediated signaling changes, resulting in immunosuppressive phenotypes of T-cells, B-cells, NK cells, dendritic cells, mast cells, macrophages, neutrophils, and NKT cells. As a result of this, adenosine levels can accumulate to over one hundred times their normal concentration in pathological tissues, such as solid tumors, which have been shown to overexpress ecto-nucleotidases, such as CD73. Adenosine has also been shown to promote tumor angiogenesis and development. An engineered bacterium that is auxotrophic for adenosine would thus exhibit enhanced tumor-targeting and colonization.

Immunostimulatory bacteria, such as Salmonella typhi, can be made auxotrophic for adenosine by deletion of the tsx gene (Bucarey et al. (2005) Infection and Immunity 73(10):6210-6219) or by deletion of purD (Husseiny (2005) Infection and Immunity 73(3):1598-1605). In the Gram negative bacteria Xanthomonas oryzae, apurD gene knockout was shown to be auxotrophic for adenosine (Park et al. (2007) FEMS Microbiol. Lett. 276:55-59). As exemplified herein, S. typhimurium strain VNP20009, is auxotrophic for adenosine due to its purI deletion, hence, further modification to render it auxotrophic for adenosine is not required. Hence, embodiments of the immunostimulatory bacterial strains, as provided herein, are auxotrophic for adenosine. Such auxotrophic bacteria selectively replicate in the tumor microenvironment, further increasing accumulation and replication of the administered bacteria in tumors and decreasing the levels of adenosine in and around tumors, thereby reducing or eliminating the immunosuppression caused by accumulation of adenosine. Exemplary of such bacteria, provided herein is a modified strain of S. typhimurium containing purI⁻/msbB⁻ mutations to provide adenosine auxotrophy.

c. Flagellin Deficient Strains

Flagella are organelles on the surface of bacteria that are composed of a long filament attached via a hook to a rotary motor that can rotate in a clockwise or counterclockwise manner to provide a means for locomotion. Flagella in S. typhimurium are important for chemotaxis and for establishing an infection via the oral route, due to the ability to mediate motility across the mucous layer in the gastrointestinal tract. While flagella have been demonstrated to be required for chemotaxis to and colonization of tumor cylindroids in vitro (Kasinskas and Forbes (2007) Cancer Res. 67(7):3201-3209), and motility has been shown to be important for tumor penetration (Toley and Forbes (2012) Integr. Biol. (Camb). 4(2): 165-176), flagella are not required for tumor colonization in animals when the bacteria are administered intravenously (Stritzker et al. (2010) International Journal of Medical Microbiology 300:449-456). Each flagellar filament is composed of tens of thousands of flagellin subunits. The S. typhimurium chromosome contains two genes, fliC and fljB, that encode antigenically distinct flagellin monomers. Mutants defective for both fliC and fljB are nonmotile and avirulent when administered via the oral route of infection, but maintain virulence when administered parenterally.

Flagellin is a major pro-inflammatory determinant of Salmonella (Zeng et al. (2003) J Immunol 171:3668-3674), and is directly recognized by TLR5 on the surface of cells, and by NLCR4 in the cytosol (Lightfield et al. (2008) Nat. Immunol. 9(10): 1171-1178). Both pathways lead to pro-inflammatory responses resulting in the secretion of cytokines, including IL-1β, IL-18, TNF-α and IL-6. Attempts have been made to make Salmonella-based cancer immunotherapy more potent by increasing the pro-inflammatory response to flagellin by engineering the bacteria to secrete Vibrio vulnificus flagellin B, which induces greater inflammation than flagellin encoded by fliC and fljB (Zheng et al. (2017) Sci. Transl. Med. 9(376):eaak9537).

Herein, Salmonella bacteria, S. typhimurium, are engineered to lack both flagellin subunits fliC and fljB, to reduce pro-inflammatory signaling. For example, as shown herein, a Salmonella strain lacking msbB, which results in reduced TNF-alpha induction, is combined with fliC and fljB knockouts. This results in a Salmonella strain that has a combined reduction in TNF-alpha induction and reduction in TLR5 recognition. These modifications can be combined with msbB⁻, fliC⁻ and fljB⁻, and transformed with an immunostimulatory plasmid, optionally containing CpGs, and a therapeutic molecule, such as an antibody or RNAi molecule(s) targeting an immune checkpoint, such as TREX1, PD-L1, VISTA, SIRP-alpha, TGF-beta, beta-catenin, CD47, VEGF, and combinations thereof. The resulting bacteria have reduced pro-inflammatory signaling, but robust anti-tumor activity.

For example, as provided herein, a fliC and fljB double mutant was constructed in the asd deleted strain of S. typhimurium VNP20009. VNP20009, which is attenuated for virulence by disruption of purI/purM, was also engineered to contain an msbB deletion that results in production of a lipid A subunit that is less toxigenic than wild-type lipid A. This results in reduced TNF-α production in the mouse model after intravenous administration, compared to strains with wild-type lipid A. The resulting strain is exemplary of strains that are attenuated for bacterial inflammation by modification of lipid A to reduce TLR2/4 signaling, and deletion of the flagellin subunits to reduce TLR5 recognition and inflammasome induction. Deletion of the flagellin subunits combined with modification of the LPS allows for greater tolerability in the host, and directs the immuno-stimulatory response towards delivery of RNA interference against desired targets in the TME which elicit an anti-tumor response and promote an adaptive immune response to the tumor.

d. Salmonella Engineered to Escape the Salmonella Containing Vacuole (SCV)

Salmonella, such as S. typhimurium, are intracellular pathogens that replicate primarily in a membrane bound compartment called a Salmonella containing vacuole (SCV). In some epithelial cell lines and at a low frequency, S. typhimurium have been shown to escape into the cytosol where they can replicate. Salmonella engineered to escape the SCV with higher efficiency will be more efficient at delivering macromolecules, such as plasmids, as the lipid bilayer of the SCV is a potential barrier. Provided herein are Salmonella and methods that have enhanced frequency of SCV escape. This is achieved by deletion of genes required for Salmonella induced filament (SIF) formation. These mutants have an increased frequency of SCV escape and can replicate in the cytosol.

For example, enhanced plasmid delivery using a sifA mutant of S. typhimurium has been demonstrated. The sifA gene encodes SPI-2, T3SS-2 secreted effector protein that mimics or activates a RhoA family of host GTPases (Ohlson et al. (2008) Cell Host & Microbe 4:434-446). Other genes encoding secreted effectors involved in SIF formation can be targeted. These include, for example, sseJ, sseL, sopD2, pipB2, sseF, sseG, spvB, and steA. Enhancing the escape of S. typhimurium by prevention of SIF formation releases live bacteria into the cytosol, where they can replicate.

Another method to enhance S. typhimurium escape from the SCV and increase the delivery of macromolecules such as plasmids, is the expression of a heterologous hemolysin that results in pore formation in, or rupture of, the SCV membrane. One such hemolysin is the Listeriolysin O protein (LLO) from Listeria monocytogenes, which is encoded by the hlyA gene. LLO is a cholesterol-dependent pore-forming cytolysin that is secreted from L. monocytogenes and is primarily responsible for phagosomal escape and entry into the cytosol of host cells. Secretion of LLO from S. typhimurium can result in bacterial escape and lead to replication in the cytosol. To prevent intact S. typhimurium from escaping the SCV and replicating in the cytosol, the nucleotides encoding the signal sequence can be removed from the gene. In this manner, the active LLO is contained within the cytoplasm of the S. typhimurium and LLO is only released when the bacteria undergo lysis. As provided herein, VNP20009 engineered to express cytoLLO to enhance delivery of plasmids for expression of interfering RNAs to targets, such as TREX1, can increase the therapeutic potency of the immunostimulatory bacteria.

e. Deletions in Salmonella Genes Required for Biofilm Formation

Bacteria and fungi are capable of forming multicellular structures called biofilms. Bacterial biofilms are encased within a mixture of secreted and cell wall-associated polysaccharides, glycoproteins, and glycolipids, as well as extracellular DNA, known collectively as extracellular polymeric substances. These extracellular polymeric substances protect the bacteria from multiple insults, such as cleaning agents, antibiotics, and antimicrobial peptides. Bacterial biofilms allow for colonization of surfaces, and are a cause of significant infection of prosthetics, such as injection ports and catheters. Biofilms can also form in tissues during the course of an infection, which leads to increases in the duration of bacterial persistence and shedding, and limits the effectiveness of antibiotic therapies. Chronic persistence of bacteria in biofilms is associated with increased tumorigenesis, for example in S. typhi infection of the gall bladder (Di Domenico et al. (2017) Int. J. Mol. Sci. 18:1887).

S. typhimurium biofilm formation is regulated by CsgD. CsgD activates the csgBAC operon, which results in increased production of the curli fimbrial subunits CsgA and CsgB (Zakikhany et al. (2010) Molecular Microbiology 77(3):771-786). CsgA is recognized as a PAMP by TLR2 and induces production of IL-8 from human macrophages (Tukel et al. (2005) Molecular Microbiology 58(1):289-304). Further, CsgD indirectly increases cellulose production by activating the adrA gene that encodes for di-guanylate cyclase. The small molecule cyclic di-guanosine monophosphate (c-di-GMP) generated by AdrA is a ubiquitous secondary messenger found in almost all bacterial species. The AdrA-mediated increase in c-di-GMP enhances expression of the cellulose synthase gene bcsA, which in turn increases cellulose production via stimulation of the bcsABZC and bcsEFG operons. Reduction in the capability of immunostimulatory bacteria such as S. typhimurium to form biofilms can be achieved through deletion of genes involved in biofilm formation such as, for example, csgD, csgA, csgB, adrA, bcsA, bcsB, bcsZ, bcsE, bcsF, bcsG, dsbA, or dsbB (Anwar et al. (2014) PLoS ONE 9(8):e106095).

S. typhimurium can form biofilms in solid tumors as protection against phagocytosis by host immune cells. Salmonella mutants that cannot form biofilms are taken up more rapidly by host phagocytic cells and are cleared from infected tumors (Crull et al. (2011) Cellular Microbiology 13(8):1223-1233). This increase in intracellular localization within phagocytic cells can reduce the persistence of extracellular bacteria, and enhance the effectiveness of plasmid delivery and gene knockdown by RNA interference as described herein. Immunostimulatory bacteria engineered to reduce biofilm formation, will increase clearance rate from tumors/tissues and therefore increase the tolerability of the therapy, and will prevent colonization of prosthetics in patients, thereby increasing the therapeutic benefit of these strains. Adenosine mimetics can inhibit S. typhimurium biofilm formation, indicating that the high adenosine concentration in the tumor microenvironment can contribute to tumor-associated biofilm formation (Koopman et al. (2015) Antimicrob. Agents Chemother. 59:76-84). As provided herein, live attenuated strains of bacteria, such as S. typhimurium, that contain a purI disruption (and therefore, colonize adenosine-rich tumors), and are also prevented from forming biofilms, by deletion of one or more genes required for biofilm formation, are engineered to deliver plasmids encoding interfering RNA to stimulate a robust anti-tumor immune response.

The adrA gene encodes a di-guanylate cyclase that produces c-di-GMP, which is required for S. typhimurium biofilm formation. c-di-GMP binds to and is an agonist for the host cytosolic protein STING. As described above, STING agonists are pursued as anti-cancer treatments, vaccine adjuvants, and bacteria engineered to secrete cyclic di-nucleotides for use in immunotherapies (Libanova 2012, Synlogic 2018 AACR poster). Immunostimulatory bacteria that are reduced in c-di-GMP production via the deletion of adrA is counterintuitive, but bacterial mutants, such as S. typhimurium mutants, that are unable to form biofilms (including an adrA mutant), have demonstrated reduced therapeutic potential in mouse tumor models (Crull et al. (2011) Cellular Microbiology 13(8):1223-1233). Several human alleles of STING are refractory to binding bacterially-produced 3′3′ CDNs (Corrales et al. (2015) Cell Reports 11:1018-1030).

As described herein, bacterial strains, such as S. typhimurium strains, that are engineered to be adenosine auxotrophic, and are reduced in their ability to induce pro-inflammatory cytokines by modification of the LPS and/or deletion of flagellin, and/or deletion of genes required for biofilm formation, and further modified to deliver interfering RNAs, promote robust anti-tumor immune responses.

f. Deletions in Genes in the LPS Biosynthetic Pathway

The LPS of Gram negative bacteria is the major component of the outer leaflet of the bacterial membrane. It is composed of three major parts, lipid A, a non-repeating core oligosaccharide, and the O antigen (or O polysaccharide). O antigen is the outermost portion on LPS and serves as a protective layer against bacterial permeability, however, the sugar composition of O antigen varies widely between strains. The lipid A and core oligosaccharide vary less, and are more typically conserved within strains of the same species. Lipid A is the portion of LPS that contains endotoxin activity. It is typically a disaccharide decorated with multiple fatty acids. These hydrophobic fatty acid chains anchor the LPS into the bacterial membrane, and the rest of the LPS projects from the cell surface. The lipid A domain is responsible for much of the toxicity of Gram-negative bacteria. Typically, LPS in the blood is recognized as a significant pathogen associated molecular pattern (PAMP) and induces a profound pro-inflammatory response. LPS is the ligand for a membrane-bound receptor complex comprising CD14, MD2 and TLR4. TLR4 is a transmembrane protein that can signal through the MyD88 and TRIF pathways to stimulate the NFκB pathway and result in the production of pro-inflammatory cytokines such as TNF-α and IL-1β, the result of which can be endotoxic shock, which can be fatal. LPS in the cytosol of mammalian cells can bind directly to the CARD domains of caspases 4, 5, and 11, leading to autoactivation and pyroptotic cell death (Hagar et al. (2015) Cell Research 25:149-150). The composition of lipid A and the toxigenicity of lipid A variants is well documented. For example, a monophosphorylated lipid A is much less inflammatory than lipid A with multiple phosphate groups. The number and length of the acyl chains on lipid A can also have a profound impact on the degree of toxicity. Canonical lipid A from E. coli has six acyl chains, and this hexa-acylation is potently toxic. S. typhimurium lipid A is similar to that of E. coli; it is a glucosamine disaccharide that carries four primary and two secondary hydroxyacyl chains (Raetz and Whitfield (2002) Annu. Rev. Biochem. 71:635-700).

As described above, msbB mutants of S. typhimurium cannot undergo the terminal myristoylation of its LPS and produce predominantly penta-acylated LPS that is significantly less toxic than hexa-acylated lipid A. The modification of lipid A with palmitate is catalyzed by palmitoyl transferase (PagP). Transcription of the pagP gene is under control of the PhoP/PhoQ system which is activated by low concentrations of magnesium, e.g., inside the SCV. Thus, the acyl content of S. typhimurium is variable, and with wild-type bacteria it can be hexa- or penta-acylated. The ability of S. typhimurium to palmitate its lipid A increases resistance to antimicrobial peptides that are secreted into phagolysozomes.

In wild type S. typhimurium, expression of pagP results in a lipid A that is hepta-acylated. In an msbB mutant (in which the terminal acyl chain of the lipid A cannot be added), the induction of pagP results in a hexa-acylated LPS (Kong et al. (2011) Infection and Immunity 79(12):5027-5038). Hexa-acylated LPS has been shown to be the most pro-inflammatory. While other groups have sought to exploit this pro-inflammatory signal, for example, by deletion of pagP to allow only hexa-acylated LPS to be produced (Felgner et al. (2016) Gut Microbes 7(2): 171-177; Felgner et al. (2018) Oncoimmunology 7(2): e1382791), this can lead to poor tolerability, due to the TNF-α-mediated pro-inflammatory nature of the LPS and paradoxically less adaptive immunity (Kocijancic et al. (2017) Oncotarget 8(30):49988-50001).

LPS is a potent TLR-4 agonist that induces TNF-α and IL-6. The dose-limiting toxicities in the I.V. VNP20009 clinical trial (Toso et al. (2002) J. Clin. Oncol. 20(1):142-152) at 1E9 CFU/m² were cytokine mediated (fever, hypotension), with TNF-α levels >100,000 pg/ml and IL-6 levels >10,000 pg/ml in serum at 2 hr. Despite the msbB deletion in VNP20009 and its reduced pyrogenicity, the LPS still can be toxic at high doses, possibly due to the presence of hexa-acylated LPS. Thus, a pagP⁻/msbB⁻ strain is better tolerated at higher doses, as it cannot produce hexa-acylated LPS, and will allow for dosing in humans at or above 1E9 CFU/m². Higher dosing can lead to increased tumor colonization, enhancing the therapeutic efficacy of the immunostimulatory bacteria.

Provided herein, are live attenuated Salmonella strains, such as the exemplary strain of S. typhimurium, that only can produce penta-acylated LPS, that contain a deletion of the msbB gene (that prevents the terminal myristoylation of lipid A, as described above), and that further are modified by deletion of pagP (preventing palmitoylation). A strain modified to produce penta-acylated LPS allows for lower levels of pro-inflammatory cytokines, increased sensitivity to antimicrobial peptides, enhanced tolerability, and increased anti-tumor immunity when further modified to express interfering RNAs against immune checkpoints such as TREX1.

g. Deletions of SPI-1 and SPI-2 Genes

As described above, pathogenesis, in certain bacterial species, including Salmonella species, such as S. typhimurium, involves a cluster of genes referred to as Salmonella pathogenicity islands (SPIs; see FIG. 22 ) The SPI designated SPI-1 mediates invasion of epithelial cells. The operons and genes and their functions are depicted in FIG. 22 . SPI-1 genes include, but are not limited to: avrA, hilA, hilD, invA, invB, invC, invE, invF, invG, invH, invI, invJ, iacP, iagB, spaO, spaP, spaQ, spaR, spaS, orgA, orgB, orgC, prgH, prgI, prgJ, prgK, sicA, sicP, sipA, sipB, sipC, sipD, sirC, sopB, sopD, sopE, sopE2, sprB, and sptP. Deletion of one or more of these genes reduces or eliminates the ability of the bacterium to infect epithelial cells, but does not affect their ability to infect or invade phagocytic cells, including phagocytic immune cells.

Salmonella invades non-phagocytic intestinal epithelial cells using a type 3 secretion system (T3SS) encoded by the Salmonella pathogenicity island 1, which forms a needle-like structure that injects effector proteins directly into the cytosol of host cells. These effector proteins lead to rearrangement of the eukaryotic cell cytoskeleton to facilitate invasion of the intestinal epithelium, and also induces proinflammatory cytokines. The SPI-1 locus includes 39 genes that encode components of this invasion system (see, FIG. 22 , reproduced from Kimbrough and Miller (2002) Microbes Infect. 4(1):75-82).

SPI-1 encodes a type 3 secretion system (T3SS) that is responsible for translocation of effector proteins into the cytosol of host cells that can cause actin rearrangements that lead to uptake of Salmonella. The SPI-1 T3SS is essential for crossing the gut epithelial layer, but is dispensable for infection when bacteria are injected parenterally. The injection of some proteins and the needle complex itself can also induce inflammasome activation and pyroptosis of phagocytic cells. This pro-inflammatory cell death can limit the initiation of a robust adaptive immune response by directly inducing the death of antigen-presenting cells (APCs), as well as modifying the cytokine milieu to prevent the generation of memory T-cells. SPI-1 genes comprise a number of operons including: sitABCD, sprB, avrA, hilC, orgABC, prgKJIH, hilD, hilA, iagB, sptP, sicC, iacP, sipADCB, sicA, spaOPQRS, invFGEABCIJ, and invH.

T3SSs are complexes that play a large role in the infectivity of Gram-negative bacteria, by injecting bacterial protein effectors directly into host cells in an ATP-dependent manner. T3SS complexes cross the inner and outer bacterial membranes and create a pore in eukaryotic cell membranes upon contact with a host cell. They consist of an exportation apparatus, a needle complex and a translocon at the tip of the needle (FIG. 22 ). The needle complex includes the needle protein PrgI, a basal body, which anchors the complex in the bacterial membranes and consists of the proteins PrgH, PrgK and InvG, and other proteins, including InvH, PrgJ (rod protein) and InvJ. The translocon, which forms the pore in the host cell, is a complex of the proteins SipB, SipC and SipD. The exportation apparatus, which allows for the translocation of the effector proteins, is comprised of the proteins SpaP, SpaQ, SpaR, SpaS, InvA, InvC and OrgB. A cytoplasmic sorting platform, which establishes the specific order of protein secretion, is composed of the proteins SpaO, OrgA and OrgB (Manon et al. (2012), Salmonella, Chapter 17, eds. Annous and Gurtler, Rijeka, pp. 339-364).

The effectors translocated into the host cell by T3SS-1 include SipA, SipC, SopB, SopD, SopE, SopE2 and SptP, which are essential for cell invasion. For example, S. typhimurium sipA mutants exhibit 60-80% decreased invasion, sipC deletion results in a 95% decrease in invasion, and sopB deletion results in a 50% decrease in invasion (Manon et al. (2012), Salmonella, Chapter 17, eds. Annous and Gurtler, Rijeka, pp. 339-364). Other effectors include AvrA, which controls Salmonella-induced inflammation. Chaperones, which bind secreted proteins and maintain them in a conformation that is competent for secretion, include SicA, InvB and SicP. Transcriptional regulators include HilA, HilD, InvF, SirC and SprB. Unclassified T3SS SPI-1 proteins, which have various functions in type III secretion, include OrgC, InvE, InvI, IacP and IagB (see, FIG. 22 , adapted from Kimbrough et al. (2002) Microbes Infect. 4(1):75-82).

Thus, the inactivation of SPI-1-dependent invasion, through the inactivation or knockout of one or more genes involved in the SPI-1 pathway, eliminates the ability of the bacteria to infect epithelial cells. These genes include, but are not limited to, one more of: avrA, hilA, hilD, invA, invB, invC, invE, invF, invG, invH, invI, invJ, iacP, iagB, spaO, spaP, spaQ, spaR, spaS, orgA, orgB, orgC, prgH, prgI, prgJ, prgK, sicA, sicP, sipA, sipB, sipC, sipD, sirC, sopB, sopD, sopE, sopE2, sprB, and sptP.

Salmonella mutants lacking the T3SS-1 have been shown to invade numerous cell lines/types, by a T3SS-1 independent invasion mechanism, involving several proteins, including the invasins Rck, PagN and HlyE. The rck operon contains 6 open reading frames: pefI, srgD, srgA, srgB, rck and srgC. pefI encodes a transcriptional regulator of the pef operon, which is involved in the biosynthesis of the Pef fimbriae. These fimbriae are involved in biofilm formation, adhesion to murine small intestine and fluid accumulation in the infant mouse. SrgA oxidizes the disulfide bond of PefA, the major structural subunit of the Pef fimbriae. srgD encodes a putative transcriptional regulator; SrgD together with PefI work to induce a synergistic negative regulation of flagellar gene expression. srgB encodes a putative outer membrane protein, and srgC encodes a putative transcriptional regulator (Manon et al. (2012), Salmonella, Chapter 17, eds. Annous and Gurtler, Rijeka, pp. 339-364).

Rck is a 17 kDa outer membrane protein encoded by the large virulence plasmid of S. enteritidis and S. typhimurium, that induces adhesion to and invasion of epithelial cells, and confers a high level of resistance to neutralization by complement, by preventing the formation of the membrane attack complex. An rck mutant exhibited a 2-3 fold decrease in epithelial cell invasion compared to the wild-type strain, while Rck overexpression leads to increased invasion. Rck induces cell entry by a receptor-mediated process, promoting local actin remodeling and weak and closely adherent membrane extensions. Thus, Salmonella can enter cells by two distinct mechanisms: the Trigger mechanism mediated by the T3SS-1 complex, and a Zipper mechanism induced by Rck (Manon et al. (2012), Salmonella, Chapter 17, eds. Annous and Gurtler, Rijeka, pp. 339-364).

The invasin PagN is an outer membrane protein that has also been shown to play a role in Salmonella invasion. pagN expression is regulated by phoP. Specific stimuli, for example, acidified macrophage phagosome environments or low Mg²⁺ concentrations, are sensed by PhoQ, which then activates PhoP to regulate specific genes. It has been shown that the deletion of pagN in S. typhimurium results in a 3-fold decrease in the invasion of enterocytes, without altering cell adhesion. Although the PagN-mediated entry mechanism is not fully understood, it has been shown that actin polymerization is required for invasion. Studies have shown that PagN is required for Salmonella survival in BALB/c mice, and that a pagN mutant is less competitive for colonizing the spleen of mice than the parent strain. Because pagN is activated by PhoP, it is mostly expressed intracellularly, where the SPI-1 island encoding T3SS-1 is downregulated. It is thus possible that bacteria exiting epithelial cells or macrophages have an optimal level of PagN expression, but have low T3SS-1 expression, which can mediate subsequent interactions with other cells encountered following host cell destruction, indicating a role for PagN in Salmonella pathogenesis (Manon et al. (2012), Salmonella, Chapter 17, eds. Annous and Gurtler, Rijeka, pp. 339-364).

hlyE shares more than 90% sequence identity with the E. coli HlyE (ClyA) hemolysin. The HlyE protein lyses epithelial cells when exported from bacterial cells via outer membrane vesicle release, and is involved in epithelial cell invasion. HlyE also is involved in the establishment of systemic Salmonella infection (Manon et al. (2012), Salmonella, Chapter 17, eds. Annous and Gurtler, Rijeka, pp. 339-364).

Elimination of the ability to infect epithelial cells also can be achieved by engineering the immunostimulatory bacteria herein to contain knockouts or deletions of genes encoding proteins involved in SPI-1-independent invasion, such as one or more of the genes rck, pagN, hlyE, pefI, srgD, srgA, srgB, and srgC.

As described herein, provided are immunostimulatory bacteria that are modified so that they do not infect epithelial cells, but retain the ability to infect phagocytic cells, including tumor-resident immune cells, thereby effectively targeting the immunostimulatory bacteria to the tumor microenvironment. This is achieved by deleting or knocking out any of the proteins in SPI-1, including, but are not limited to, deletions of one more of: avrA, hilA, hilD, invA, invB, invC, invE, invF, invG, invH, invI, invJ, iacP, iagB, spaO, spaP, spaQ, spaR, spaS, orgA, orgB, orgC, prgH, prgI, prgK, sicA, sicP, sipA, sipB, sipC, sipD, sirC, sopB, sopD, sopE, sopE2, sprB, and sptP, as well as one or more of rck, pagN, hlyE, pefI, srgD, srgA, srgB, and srgC.

The immunostimulatory bacteria that do not infect epithelial cells can be further modified as described here to encode products that stimulate the immune system, including, for example, cytokines. The bacteria generally have an asd deletion to render them unable to replicate in a mammalian host.

For example, provided are strains of S. typhimurium modified by deletion of one or more SPI-1 genes, and also modified by one or more of a purI deletion, an msbB deletion, and an asd deletion, and by delivering plasmids encoding proteins that stimulate the immune system, such as genes encoding immunostimulatory cytokines. For example, bacteria with deletions of a regulatory gene (e.g., hilA or invF) required for expression of the SPI-1-associated type 3 secretion system (T3SS-1), a T3SS-1 structural gene (e.g., invG or prgH), and/or a T3SS-1 effector gene (e.g., sipA or avrA) are provided. As discussed above, this secretion system is responsible for injecting effector proteins into the cytosol of non-phagocytic host cells such as epithelial cells that cause the uptake of the bacteria; deletion of one or more of these genes eliminates infection/invasion of epithelial cells. Deletion of one or more of the genes, such as hilA, provides immunostimulatory bacteria that can be administered intravenously or intratumorally, resulting in infection of phagocytic cells, which do not require the SPI-1 T3SS for uptake, and also prolongs the longevity of these phagocytic cells. The hilA mutation also reduces the quantity of pro-inflammatory cytokines, increasing the tolerability of the therapy, as well as the quality of the adaptive immune response.

Salmonella also have a Salmonella pathogenicity island 2 (SPI-2), encoding another T3SS that is activated following entry of the bacterium into the host cell, and interferes with phagosome maturation, resulting in the formation of a specialized Salmonella-containing vacuole (SCV), where the Salmonella resides during intracellular survival and replication. SPI-2 T3SS effectors include SseB, SseC, SseD and SpiC, which are responsible for assembly of the F-actin coat around intracellular bacteria; this actin coat promotes fusion of the SCV with actin-containing or actin-propelled vesicles, and prevents it from fusing with unfavorable compartments. SifA is responsible for the formation of Salmonella-induced filaments (SIFs), which are tubules that connect the individual SCVs in the infected cell. sifA is essential to maintaining the integrity of the SCV, and sifA mutants are released into the cytosol of host cells. SseF and SseG are components of the SPI-2 T3SS that are involved in SCV positioning and cellular trafficking processes that direct materials required for the bacterium's survival and replication to the SCV. SseF and SseG also are involved in SIF formation. Other SPI-2 T3SS effectors include PipB2, SopD2, and SseJ, which are involved in SIF and SCV formation, and maintenance of vacuole integrity; SpvC, SseL, and SspH1, which are involved in host immune signaling; and SteC, SspH2, SrfH/SseI and SpvB, which are involved in the formation of the SCV F-actin meshwork, in the migration of infected phagocytes, in the inhibition of actin polymerization, and in P-body disassembly in infected cells (Coburn et al. (2007) Clinical Microbiology Reviews 20(4):535-549; Figueira and Holden (2012) Microbiology 158:1147-1161).

The immunostimulatory bacteria herein can include deletions or modifications in any of the SPI-2 T3SS genes that affect the formation or integrity of the SCV and associated structures, such as SIFs. These mutants have an increased frequency of SCV escape and can replicate in the cytosol. For example, immunostimulatory bacteria, such as Salmonella species, engineered to escape the SCV are more efficient at delivering macromolecules, such as plasmids, as the lipid bilayer of the SCV is a potential barrier. This is achieved by deletion or mutation of genes required for Salmonella induced filament (SIF) formation, including, for example, sifA, sseJ, sseL, sopD2, pipB2, sseF, sseG, spvB, and steA.

The immunostimulatory bacteria that can escape the SCV can be further modified as described here to encode products that stimulate the immune system, including, for example, cytokines. The bacteria generally have an asd deletion to render them unable to replicate in a mammalian host.

h. Endonuclease (endA) Mutations to Increase Plasmid Delivery

The endA gene (for example, SEQ ID NO:250) encodes an endonuclease (for example, SEQ ID NO:251) that mediates degradation of double stranded DNA in the periplasm of Gram negative bacteria. Most common strains of laboratory E. coli are endA−, as a mutation in the endA gene allows for higher yields of plasmid DNA. This gene is conserved among species. To facilitate intact plasmid DNA delivery, the endA gene of the engineered immunostimulatory bacteria is deleted or mutated to prevent its endonuclease activity. Exemplary of such mutations is an E208K amino acid substitution (Durfee, et al. (2008) J. Bacteriol. 190(7):2597-2606) or a corresponding mutation in the species of interest. endA, including E208, is conserved among bacterial species, including Salmonella. Thus, the E208K mutation can be used to eliminate endonuclease activity in other species, including Salmonella species. Those of skill in the art can introduce other mutations or deletions to eliminate endA activity. Effecting this mutation or deleting or disrupting the gene to eliminate activity of the endA in the immunostimulatory bacteria herein, such as in Salmonella, increases efficiency of intact plasmid DNA delivery, thereby increasing expression of the RNAs, such as the shRNA and/or miRNA, targeting any or two or more of the immune checkpoints, encoded in the plasmid, thereby increasing RNAi-mediated knockdown of checkpoint genes and enhancing anti-tumor efficacy.

i. RIG-I Inhibition

Of the TLR-independent type I IFN pathways, one is mediated by host recognition of single-stranded (ss) and double-stranded (ds) RNA in the cytosol. These are sensed by RNA helicases, including retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA-5), and through the IFN-β promoter stimulator 1 (IPS-1) adaptor protein-mediated phosphorylation of the IRF-3 transcription factor, leading to induction of type I IFN (Ireton and Gale (2011) Viruses 3(6):906-919). RIG-I recognizes dsRNA and ssRNA bearing 5′-triphosphates. This moiety can directly bind RIG-I, or be synthesized from a poly(dA-dT) template by the poly DNA-dependent RNA polymerase III (Pol III) (Chiu, Y. H. et al. (2009) Cell 138(3):576-91). A poly(dA-dT) template containing two AA dinucleotide sequences occurs at the U6 promoter transcription start site in a common lentiviral shRNA cloning vector. Its subsequent deletion in the plasmid prevents type I IFN activation (Pebernard et al. (2004) Differentiation. 72:103-111). A RIG-I binding sequence can be included in the plasmids provided herein; inclusion can increase immunostimulation that increases anti-tumoral activity of the immunostimulatory bacteria herein.

j. DNase II Inhibition

Another nuclease responsible for degrading foreign and self DNA is DNase II, an endonuclease, which resides in the endosomal compartment and degrades DNA following apoptosis. Lack of DNase II (Dnase2a in mice) results in the accumulation of endosomal DNA that escapes to the cytosol and activates cGAS/STING signaling (Lan Y Y et al. (2014) Cell Rep. 9(1):180-192). Similar to TREX1, DNase II-deficiency in humans presents with autoimmune type I interferonopathies. In cancer, dying tumor cells that are engulfed by tumor-resident macrophages prevent cGAS/STING activation and potential autoimmunity through DNase II digestion of DNA within the endosomal compartment (Ahn et al. (2018) Cancer Cell 33:862-873). Hence, embodiments of the immunostimulatory bacterial strains, as provided herein, encode RNAi, such as shRNA or miRNA that inhibit, suppress or disrupt expression of DNase II, which can inhibit DNase II in the tumor microenvironment, thereby provoking accumulation of endocytosed apoptotic tumor DNA in the cytosol, where it can act as a potent cGAS/STING agonist

k. RNase H2 Inhibition

While TREX1 and DNase II function to clear aberrant DNA accumulation, RNase H2 functions similarly to eliminate pathogenic accumulation of RNA:DNA hybrids in the cytosol. Similar to TREX1, deficiencies in RNase H2 also contribute to the autoimmune phenotype of Aicardi-Goutières syndrome (Rabe, B. (2013) J. Mol. Med. 91:1235-1240). Specifically, loss of RNase H2 and subsequent accumulation of RNA:DNA hybrids or genome-embedded ribonucleotide substrates has been shown to activate cGAS/STING signaling (Mackenzie et al. (2016) EMBO J. 35(8):831-44). Hence, embodiments of the immunostimulatory bacterial strains, as provided herein, encode RNAi, such as shRNA or miRNA that inhibit, suppress or disrupt expression of RNase H2, to thereby inhibit RNase H2, resulting in tumor-derived RNA:DNA hybrids and derivatives thereof, which activate cGAS/STING signaling and anti-tumor immunity.

l. Stabilin-1/CLEVER-1 Inhibition

Another molecule expressed primarily on monocytes and involved in regulating immunity is stabilin-1 (gene name STAB1, also known as CLEVER-1, FEEL-1). Stabilin-1 is a type I transmembrane protein that is upregulated on endothelial cells and macrophages following inflammation, and in particular, on tumor-associated macrophages (Kzhyshkowska et al. (2006) J. Cell. Mol. Med. 10(3):635-649). Upon inflammatory activation, stabilin-1 acts as a scavenger and aids in wound healing and apoptotic body clearance, and can prevent tissue injury, such as liver fibrosis (Rantakari et al. (2016) Proc. Natl. Acad. Sci. USA 113(33):9298-9303). Upregulation of stabilin-1 directly inhibits antigen-specific T cell responses, and knockdown by siRNA in monocytes was shown to enhance their pro-inflammatory function (Palani, S. et al. (2016) J. Immunol. 196:115-123). Hence, embodiments of the immunostimulatory bacterial strains, as provided herein, encode RNAi, such as shRNA or miRNA that inhibit, suppress or disrupt expression of Stabilin-1/CLEVER-1 in the tumor microenvironment, thereby enhancing the pro-inflammatory functions of tumor-resident macrophages.

5. Immunostimulatory Proteins

The immunostimulatory bacteria herein can be modified to encode an immunostimulatory protein that promotes or induces or enhances an anti-tumor response. The immunostimulatory protein can be encoded on a plasmid in the bacterium, under the control of a eukaryotic promoter, such as a promoter recognized by RNA polymerase II, for expression in a eukaryotic subject, particularly the subject for whom the immunostimulatory bacterium is to be administered, such as a human. The nucleic acid encoding the immunostimulatory protein can include, in addition to the eukaryotic promoter, other regulatory signals for expression or trafficking in the cells, such as for secretion or expression on the surface of a cell.

Immunostimulatory proteins are those that, in the appropriate environment, such as a tumor microenvironment (TME), can promote or participate in or enhance an anti-tumor response by the subject to whom the immunostimulatory bacterium is administered. Immunostimulatory proteins include, but are not limited to, cytokines, chemokines and co-stimulatory molecules. These include cytokines, such as, but not limited to, IL-2, IL-7, IL-12, IL-15, and IL-18; chemokines, such as, but not limited to, CCL3, CCL4, CCL5, CXCL9, CXCL10, and CXCL11; and/or co-stimulatory molecules, such as, but not limited to, CD40, CD40L, OX40, OX40L, 4-1BB, 4-1BBL, members of the TNF/TNFR superfamily and members of the B7-CD28 family. Other such immunostimulatory proteins that are used for treatment of tumors or that can promote, enhance or otherwise increase or evoke an anti-tumor response, known to those of skill in the art, are contemplated for encoding in the immunostimulatory bacteria provided herein.

The genome of the immunostimulatory bacteria provided herein also can be modified to increase or promote infection of immune cells, particularly immune cells in the tumor microenvironment, such as phagocytic cells. The bacteria also can be modified to decrease pyroptosis in immune cells. The immunostimulatory bacteria include those, for example, that have modifications that disrupt/inhibit the SPI-1 pathway, such as disruption or deletion of hilA, and/or disruption/deletion of flagellin genes, rod protein, needle protein, and/or pagP as detailed and exemplified elsewhere herein.

Immunostimulatory Bacteria Encoding Cytokines and Chemokines

In some embodiments, the immunostimulatory bacteria herein are engineered to express cytokines to stimulate the immune system, including, but not limited to, IL-2, IL-7, IL-12 (IL-12p70 (IL12p40+IL-12p35)), IL-15 (and the IL-15:IL-15R alpha chain complex), and IL-18. Cytokines stimulate immune effector cells and stromal cells at the tumor site, and enhance tumor cell recognition by cytotoxic cells. In some embodiments, the immunostimulatory bacteria can be engineered to express chemokines, such as, for example, CCL3, CCL4, CCL5, CXCL9, CXCL10 and CXCL11.

IL-2

Interleukin-2 (IL-2), which was the first cytokine approved for the treatment of cancer, is implicated in the activation of the immune system by several mechanisms, including the activation and promotion of CTL growth, the generation of lymphokine-activated killer (LAK) cells, the promotion of Treg cell growth and proliferation, the stimulation of TILs, and the promotion of T cell, B cell and NK cell proliferation and differentiation. Recombinant IL-2 (rIL-2) is FDA-approved for the treatment of metastatic renal cell carcinoma (RCC) and metastatic melanoma (Sheikhi et al. (2016) Iran J. Immunol. 13(3):148-166).

IL-7

IL-7, which is a member of the IL-2 superfamily, is implicated in the survival, proliferation and homeostasis of T cells. Mutations in the IL-7 receptor have been shown to result in the loss of T cells, and the development of severe combined immunodeficiency (SCID), highlighting the critical role that IL-7 plays in T cell development. IL-7 is a homeostatic cytokine that provides continuous signals to resting naïve and memory T cells, and which accumulates during conditions of lymphopenia, leading to an increase in both T cell proliferation and T cell repertoire diversity. In comparison to IL-2, IL-7 is selective for expanding CD8⁺ T cells over CD4⁺FOXP3⁺ regulatory T cells. Recombinant IL-7 has been shown to augment antigen-specific T cell responses following vaccination and adoptive cell therapy in mice. IL-7 also can play a role in promoting T-cell recovery following chemotherapy of hematopoietic stem cell transplantation. Early phase clinical trials on patients with advanced malignancy have shown that recombinant IL-7 is well-tolerated and has limited toxicity at biologically active doses (i.e., in which the numbers of circulating CD4⁺ and CD8⁺ T cells increased by 3-4 fold) (Lee, S. and Margolin, K. (2011) Cancers 3:3856-3893). IL-7 has been shown to possess antitumor effects in tumors such as gliomas, melanomas, lymphomas, leukemia, prostate cancer and glioblastoma, and the in vivo administration of IL-7 in murine models resulted in decreased cancer cell growth. IL-7 also has been shown to enhance the antitumor effects of IFN-γ in rat glioma tumors, and to induce the production of IL-1α, IL-1β and TNF-α by monocytes, which results in the inhibition of melanoma growth. Additionally, administration of recombinant IL-7 following the treatment of pediatric sarcomas resulted in the promotion of immune recovery (Lin et al. (2017) Anticancer Research 37:963-968).

IL-12 (IL-12p70 (IL-12p40+IL-12p35)

Bioactive IL-12 (IL-12p70), which promotes cell-mediated immunity, is a heterodimer, composed of p35 and p40 subunits, whereas IL-12p40 monomers and homodimers act as IL-12 antagonists. IL-12, which is secreted by antigen-presenting cells, promotes the secretion of IFN-γ from NK and T cells, inhibits tumor angiogenesis, results in the activation and proliferation of NK cells, CD8⁺ T cells and CD4⁺ T cells, enhances the differentiation of CD4⁺ Th0 cells into Th1 cells, and promotes antibody-dependent cell-mediated cytotoxicity (ADCC) against tumor cells. IL-12 has been shown to exhibit antitumor effects in murine models of melanoma, colon carcinoma, mammary carcinoma and sarcoma (Kalinski et al. (2001) Blood 97:3466-3469; Sheikhi et al. (2016) Iran J. Immunol. 13(3):148-166; Lee, S. and Margolin, K. (2011) Cancers 3:3856-3893).

IL-15 and IL-15:IL-15Rα

IL-15 is structurally similar to IL-2, and while both IL-2 and IL-15 provide early stimulation for the proliferation and activation of T cells, IL-15 blocks IL-2 induced apoptosis, which is a process that leads to the elimination of stimulated T cells and induction of T-cell tolerance, limiting memory T cell responses and potentially limiting the therapeutic efficacy of IL-2 alone. IL-15 also supports the persistence of memory CD8⁺ T cells for maintaining long-term antitumor immunity, and has demonstrated significant antitumor activity in pre-clinical murine models via the direct activation of CD8⁺ effector T cells in an antigen-independent manner. In addition to CD8⁺ T cells, IL-15 is responsible for the development, proliferation and activation of effector natural killer (NK) cells (Lee, S. and Margolin, K. (2011) Cancers 3:3856-3893; Han et al. (2011) Cytokine 56(3):804-810).

IL-15 and IL-15 receptor alpha (IL-15Rα) are coordinately expressed by antigen-presenting cells such as monocytes and dendritic cells, and IL-15 is presented in trans by IL-15Rα to the IL-15Rβγ_(C) receptor complex expressed on the surfaces of CD8⁺ T cells and NK cells. Soluble IL-15:IL15-Rα complexes have been shown to modulate immune responses via the IL-15Rβγ_(C) complex, and the biological activity of IL-15 has been shown to be increased 50-fold by administering it in a preformed complex of IL-15 and soluble IL-15Rα, which has an increased half-life compared to IL-15 alone. This significant increase in the therapeutic efficacy of IL-15 by pre-association with IL-15Rα has been demonstrated in murine tumor models (Han et al. (2011) Cytokine 56(3):804-810).

IL-18

IL-18 induces the secretion of IFN-γ by NK and CD8⁺ T cells, enhancing their toxicity. IL-18 also activates macrophages and stimulates the development of Th1 helper CD4⁺ T cells. IL-18 has shown promising anti-tumor activity in several preclinical mouse models. For example, administration of recombinant IL-18 (rIL-18) resulted in the regression of melanoma or sarcoma in syngeneic mice through the activation of CD4⁺ T cells and/or NK cell-mediated responses. Other studies showed that IL-18 anti-tumor effects were mediated by IFN-γ and involved antiangiogenic mechanisms. The combination of IL-18 with other cytokines, such as IL-12, or with co-stimulatory molecules, such as CD80, enhances the IL-18-mediated anti-tumor effects. Phase I clinical trials in patients with advanced solid tumors and lymphomas showed that IL-18 administration was safe, and that it resulted in immune modulatory activity and in the increase of serum IFN-γ and GM-CSF levels in patients and modest clinical responses. Clinical trials showed that IL-18 can be combined with other anticancer therapeutic agents, such as monoclonal antibodies, cytotoxic drugs or vaccines (Fabbi et al. (2015) J. Leukoc. Biol. 97:665-675; Lee, S. and Margolin, K. (2011) Cancers 3:3856-3893).

It was found that an attenuated strain of Salmonella typhimurium, engineered to express IL-18, inhibited the growth of s.c. tumors or pulmonary metastases in syngeneic mice without any toxic effects following systemic administration. Treatment with this engineered bacterium induced the accumulation of T cells, NK cells and granulocytes in tumors, and resulted in the intratumoral production of cytokines (Fabbi et al. (2015) J. Leukoc. Biol. 97:665-675).

Chemokines

Chemokines are a family of small cytokines that mediate leukocyte migration to areas of injury or inflammation and are involved in mediating immune and inflammatory responses. Chemokines are classified into four subfamilies, based on the position of cysteine residues in their sequences, namely XC-, CC-, CXC- and CX3C-chemokine ligands, or XCL, CCL, CXCL and CX3CL. The chemokine ligands bind to their cognate receptors and regulate the circulation, homing and retention of immune cells, with each chemokine ligand-receptor pair selectively regulating a certain type of immune cell. Different chemokines attract different leukocyte populations, and form a concentration gradient in vivo, with attracted immune cells moving through the gradient towards the higher concentration of chemokine (Argyle D. and Kitamura, T. (2018) Front. Immunol. 9:2629; Dubinett et al. (2010) Cancer J. 16(4):325-335). Chemokines can improve the antitumor immune response by increasing the infiltration of immune cells into the tumor, and facilitating the movement of antigen-presenting cells (APCs) to tumor-draining lymph nodes, which primes naïve T cells and B cells (Lechner et al. (2011) Immunotherapy 3(11): 1317-1340). The immunostimulatory bacteria herein can be engineered to encode chemokines, including, but not limited to, CCL3, CCL4, CCL5, CXCL9, CXCL10 and CXCL11.

CCL3, CCL4, CCL5

CCL3, CCL4 and CCL5 share a high degree of homology, and bind to CCR5 (CCL3, CCL4 and CCL5) and CCR1 (CCL3 and CCL5) on several cell types, including immature DCs and T cells, in both humans and mice. Therapeutic T cells have been shown to induce chemotaxis of innate immune cells to tumor sites, via the tumor-specific secretion of CCL3, CCL4 and CCL5 (Dubinett et al. (2010) Cancer J. 16(4):325-335).

The induction of the T helper cell type 1 (Th1) response releases CCL3. In vivo and in vitro studies of mice have indicated that CCL3 is chemotactic for both neutrophils and monocytes; specifically, CCL3 can mediate myeloid precursor cell (MPC) mobilization from the bone marrow, and has MPC regulatory and stimulatory effects. Human ovarian carcinoma cells transfected with CCL3 showed enhanced T cell infiltration and macrophages within the tumor, leading to an improved antitumor response, and indicated that CCL3-mediated chemotaxis of neutrophils suppressed tumor growth. DCs transfected with the tumor antigen human melanoma-associated gene (MAGE)-1 that were recruited by CCL3 exhibited superior anti-tumor effects, including increased lymphocyte proliferation, cytolytic capacity, survival, and decreased tumor growth in a mouse model of melanoma. A combinatorial use of CCL3 with an antigen-specific platform for MAGE-1 has also been used in the treatment of gastric cancer. CCL3 production by CT26, a highly immunogenic murine colon tumor, slowed in vivo tumor growth; this process was indicated to be driven by the CCL3-dependent accumulation of natural killer (NK) cells, and thus, IFNγ, resulting in the production of CXCL9 and CXLC10 (Allen et al. (2017) Oncoimmunology 7(3):e1393598; Schaller et al. (2017) Expert Rev. Clin. Immunol. 13(11):1049-1060).

CCL3 has been used as an adjuvant for the treatment of cancer. Administration of a CCL3 active variant, ECI301, after radiofrequency ablation in mouse hepatocellular carcinoma increased tumor-specific responses, and this mechanism was further shown to be dependent on the expression of CCR1. CCL3 has also shown success as an adjuvant in systemic cancers, whereby mice vaccinated with CCL3 and IL-2 or granulocyte-macrophage colony-stimulating factor (GM-CSF) in a model of leukemia/lymphoma exhibited increased survival (Schaller et al. (2017) Expert Rev. Clin. Immunol. 13(11): 1049-1060).

CCL3 and CCL4 play a role in directing CD8⁺ T cell infiltration into primary tumor sites in melanoma and colon cancers. Tumor production of CCL4 leads to the accumulation of CD103⁺ DCs; suppression of CCL4 through a WNT/β-catenin-dependent pathway prevented CD103⁺ DC infiltration of melanoma tumors (Spranger et al. (2015) Nature 523(7559):231-235). CCL3 was also shown to enhance CD4⁺ and CD8⁺ T cell infiltration to the primary tumor site in a mouse model of colon cancer (Allen et al. (2017) Oncoimmunology 7(3):e1393598).

The binding of CCL3 or CCL5 to their receptors (CCR1 and CCR5, respectively), moves immature DCs, monocytes and memory and T effector cells from the circulation into sites of inflammation or infection. For example, CCL5 expression in colorectal tumors contributes to T lymphocyte chemoattraction and survival. CCL3 and CCL5 have been used alone or in combination therapy to induce tumor regression and immunity in several preclinical models. For example, studies have shown that the subcutaneous injection of Chinese hamster ovary cells genetically modified to express CCL3 resulted in tumor inhibition and neutrophilic infiltration. In another study, a recombinant oncolytic adenovirus expression CCL5 (Ad-RANTES-E1A) resulted in primary tumor regression and blocked metastasis in a mammary carcinoma murine model (Lechner et al. (2011) Immunotherapy 3(11): 1317-1340).

In a translational study of colorectal cancer, CCL5 induced an “antiviral response pattern” in macrophages. As a result of CXCR3 mediated migration of lymphocytes at the invasive margin of liver metastases in colorectal cancer, CCL5 is produced. Blockade of CCR5, the CCL5 receptor, results in tumor death, driven by macrophages producing IFN and reactive oxygen species. While macrophages are present in the tumor microenvironment, CCR5 inhibition induces a phenotypic shift from an M2 to an M1 phenotype. CCR5 blockade also leads to clinical responses in colorectal cancer patients (Halama et al. (2016) Cancer Cell 29(4):587-601).

CCL3, CCL4 and CCL5 can be used treating conditions including lymphatic tumors, bladder cancer, colorectal cancer, lung cancer, melanoma, pancreatic cancer, ovarian cancer, cervical cancer or liver cancer (U.S. Patent Publication No. US 2015/0232880; International Patent Publication Nos. WO 2015/059303, WO 2017/043815, WO 2017/156349 and WO 2018/191654).

CXCL9, CXCL10, CXCL11

CXCL9 (MIG), CXCL10 (IP10) and CXCL11 (ITAC) are induced by the production of IFN-γ. These chemokines bind CXCR3, preferentially expressed on activated T cells, and function both angiostatically and in the recruitment and activation of leukocytes. Prognosis in colorectal cancer is strongly correlated to tumor-infiltrating T cells, particularly Th1 and CD8⁺ effector T cells; high intratumoral expression of CXCL9, CXCL10 and CXCL11 is indicative of good prognosis. For example, in a sample of 163 patients with colon cancer, those with high levels of CXCL9 or CXCL11 showed increased post-operative survival, and patients with high CXC expression had significantly higher numbers of CD3⁺ T-cells, CD4⁺ T-helper cells, and CD8⁺ cytotoxic T-cells. In liver metastases of colorectal cancer patients, CXCL9 and CXCL10 levels were increased at the invasive margin and correlated with effector T cell density. The stimulation of lymphocyte migration via the action of CXCL9 and CXCL10 on CXCR3 leads to the production of CCL5 at the invasive margin (Halama et al. (2016) Cancer Cell 29(4):587-601; Kistner et al. (2017) Oncotarget 8(52):89998-90012).

In vivo, CXCL9 functions as a chemoattractant for tumor-infiltrating lymphocytes, activated peripheral blood lymphocytes, natural killer (NK) cells and Th1 lymphocytes. CXCL9 also is critical for T cell-mediated suppression of cutaneous tumors. For example, when combined with systemic IL-2, CXCL9 has been shown to inhibit tumor growth via the increased intratumoral infiltration of CXCR3⁺ mononuclear cells. In a murine model of colon carcinoma, a combination of the huKS1/4-IL-2 fusion protein with CXCL9 gene therapy achieved a superior anti-tumor effect and prolonged lifespan through the chemoattraction and activation of CD8⁺ and CD4⁺ T lymphocytes (Dubinett et al. (2010) Cancer J. 16(4):325-335; Ruehlmann et al. (2001) Cancer Res. 61(23):8498-8503).

CXCL10, produced by activated monocytes, fibroblasts, endothelial cells and keratinocytes, is chemotactic for activated T cells and can act as an inhibitor of angiogenesis in vivo. Expression of CXCL10 in colorectal tumors has been shown to contribute to cytotoxic T lymphocyte chemoattraction and longer survival. The administration of immunostimulatory cytokines, such as IL-12, has been shown to enhance the antitumor effects generated by CXCL10. A DC vaccine primed with a tumor cell lysate and transfected with CXCL10 had increased immunological protection and effectiveness in mice; the animals showed a resistance to a tumor challenge, a slowing of tumor growth and longer survival time. In vivo and in vitro studies in mice using the CXCL10-mucin-GPI fusion protein resulted in tumors with higher levels of recruited NK cells compared to tumors not treated with the fusion protein. Interferons (which can be produced by plasmacytoid dendritic cells; these cells are associated with primary melanoma lesions and can be recruited to a tumor site by CCL20) can act on tumor DC subsets, for example, CD103⁺ DCs, which have been shown to produce CXCL9/10 in a mouse melanoma model and were associated with CXCL9/10 in human disease. CXCL10 also has shown higher expression in human metastatic melanoma samples relative to primary melanoma samples. Therapeutically, adjuvant IFN-α melanoma therapy upregulates CXCL10 production, whereas the chemotherapy agent cisplatin induces CXCL9 and CXCL10 (Dubinett et al. (2010) Cancer J. 16(4):325-335; Kuo et al. (2018) Front. Med. (Lausanne) 5:271; Li et al. (2007) Scand. J. Immunol. 65(1):8-13; Muenchmeier et al. (2013) PLoS One 8(8):e72749).

CXCL10/11 and CXCR3 expression has been established in human keratinocytes derived from basal cell carcinomas (BCCs). CXCL11 also is capable of promoting immunosuppressive indoleamine 2,3-dioxygenase (IDO) expression in human basal cell carcinoma as well as enhancing keratinocyte proliferation, which could reduce the anti-tumor activity of any infiltrating CXCR3⁺ effector T cells (Kuo et al. (2018) Front. Med. (Lausanne) 5:271).

CXCL9, CXCL10 and CXCL11 can be encoded in oncolytic viruses for treating cancer (U.S. Patent Publication No. US 2015/0232880; International Patent Publication No. WO 2015/059303). Pseudotyped oncolytic viruses or a genetically engineered bacterium encoding the gene for CXCL10 also can be used to treat cancer (International Patent Publication Nos. WO 2018/006005 and WO 2018/129404).

Co-Stimulatory Molecules

Co-stimulatory molecules enhance the immune response against tumor cells, and co-stimulatory pathways are inhibited by tumor cells to promote tumorigenesis. The immunostimulatory bacteria herein can be engineered to express co-stimulatory molecules, such as, for example, CD40, CD40L, 4-1BB, 4-1BBL, OX40 (CD134), OX40L (CD252), other members of the TNFR superfamily (e.g., CD27, GITR, CD30, Fas receptor, TRAIL-R, TNF-R, HVEM, RANK), B7 and CD28. The immunostimulatory bacteria herein also can be engineered to express agonistic antibodies against co-stimulatory molecules to enhance the anti-tumor immune response.

TNF Receptor Superfamily

The TNF superfamily of ligands (TNFSF) and their receptors (TNFRSF) are involved in the proliferation, differentiation, activation and survival of tumor and immune effector cells. Members of this family include CD30, Fas-L, TRAIL-R and TNF-R, which induce apoptosis, and CD27, OX40L, CD40L, GITR-L and 4-1BBL, which regulate B and T cell immune responses. Other members include herpesvirus entry mediator (HVEM) and CD27. The expression of TNFSF and TNFRSF by the immunostimulatory bacteria herein can enhance the antitumor immune response. It has been shown, for example, that the expression of 4-1BBL in murine tumors enhances immunogenicity, and intratumoral injection of dendritic cells (DCs) with increased expression of OX40L can result in tumor rejection in murine models. Studies have also shown that injection of an adenovirus expressing recombinant GITR into B16 melanoma cells promotes T cell infiltration and reduces tumor volume. Stimulatory antibodies against molecules such as 4-1BB, OX40 and GITR also can be encoded by the immunostimulatory bacteria to stimulate the immune system. For example, agonistic anti-4-1BB monoclonal antibodies have been shown to enhance anti-tumor CTL responses, and agonistic anti-OX40 antibodies have been shown to increase anti-tumor activity in transplantable tumor models. Additionally, agonistic anti-GITR antibodies have been shown to enhance anti-tumor responses and immunity (Lechner et al. (2011) Immunotherapy 3(11):1317-1340; Peggs et al. (2009) Clinical and Experimental Immunology 157:9-19).

CD40 and CD40L

CD40, which is a member of the TNF receptor superfamily, is expressed by APCs and B cells, while its ligand, CD40L (CD154), is expressed by activated T cells. Interaction between CD40 and CD40L stimulates B cells to produce cytokines, resulting in T cell activation and tumor cell death. Studies have shown that antitumor immune responses are impaired with reduced expression of CD40L on T cells or CD40 on dendritic cells. CD40 is expressed on the surface of several B-cell tumors, such as follicular lymphoma, Burkitt lymphoma, lymphoblastic leukemia, and chronic lymphocytic leukemia, and its interaction with CD40L has been shown to increase the expression of B7.1/CD80, B7.2/CD86 and HLA class II molecules in the CD40⁺ tumor cells, as well as enhance their antigen-presenting abilities. Transgenic expression of CD40L in a murine model of multiple myeloma resulted in the induction of CD4⁺ and CD8⁺ T cells, local and systemic antitumor immune responses and reduced tumor growth. Anti-CD40 agonistic antibodies also induced anti-tumor T cell responses (Marin-Acevedo et al. (2018) Journal of Hematology & Oncology 11:39; Dotti et al. (2002) Blood 100(1):200-207; Murugaiyan et al. (2007) J. Immunol. 178:2047-2055).

4-1BB and 4-1BBL

4-1BB (CD137) is an inducible co-stimulatory receptor that is expressed by T cells, NK cells and APCs, including DCs, B cells and monocytes, which binds its ligand, 4-1BBL to trigger immune cell proliferation and activation. 4-1BB results in longer and more wide spread responses of activated T cells. Anti-4-1BB agonists and 4-1BBL fusion proteins have been shown to increase immune-mediated antitumor activity, for example, against sarcoma and mastocytoma tumors, mediated by CD4⁺ and CD⁺ T cells and tumor-specific CTL activity (Lechner et al. (2011) Immunotherapy 3(11): 1317-1340; Marin-Acevedo et al. (2018) Journal of Hematology & Oncology 11:39).

OX40 and OX40L

OX40 (CD134) is a member of the TNF receptor superfamily that is expressed on activated effector T cells, while its ligand, OX40L is expressed on APCs, including DCs, B cells and macrophages, following activation by TLR agonists and CD40-CD40L signaling. OX40-OX40L signaling results in the activation, potentiation, proliferation and survival of T cells, as well as the modulation of NK cell function and inhibition of the suppressive activity of Tregs. Signaling through OX40 also results in the secretion of cytokines (IL-2, IL-4, IL-5 and IFN-γ), boosting Th1 and Th2 cell responses. The recognition of tumor antigens by TILs results in increased expression of OX40 by the TILs, which has been correlated with improved prognosis. Studies have demonstrated that treatment with anti-OX40 agonist antibodies or Fc-OX40L fusion proteins results in enhanced tumor-specific CD4⁺ T cell responses and increased survival in murine models of melanoma, sarcoma, colon carcinoma and breast cancer, while Fc-OX40L incorporated into tumor cell vaccines protected mice from subsequent challenge with breast carcinoma cells (Lechner et al. (2011) Immunotherapy 3(11): 1317-1340; Marin-Acevedo et al. (2018) Journal of Hematology & Oncology 11:39).

B7-CD28 Family

CD28 is a costimulatory molecule expressed on the surface of T cells that acts as a receptor for B7-1 (CD80) and B7-2 (CD86), which are co-stimulatory molecules expressed on antigen-presenting cells. CD28-B7 signaling is required for T cell activation and survival, and prevention of T cell anergy, and results in the production of interleukins such as IL-6.

Optimal T-cell priming requires two signals: (1) T-cell receptor (TCR) recognition of MHC-presented antigens and (2) co-stimulatory signals resulting from the ligation of T-cell CD28 with B7-1 (CD80) or B7-2 (CD86) expressed on APCs. Following T cell activation, CTLA-4 receptors are induced, which then outcompete CD28 for binding to B7-1 and B7-2 ligands. Antigen presentation by tumor cells is poor due to their lack of expression of costimulatory molecules such as B7-1/CD80 and B7-2/CD86, resulting in a failure to activate the T-cell receptor complex. As a result, upregulation of these molecules on the surfaces of tumor cells can enhance their immunogenicity. Immunotherapy of solid tumors and hematologic malignancies has been successfully induced by B7, for example, via tumor cell expression of B7, or soluble B7-immunoglobulin fusion proteins. The viral-mediated tumor expression of B7, in combination with other co-stimulatory ligands such as ICAM-3 and LFA-3, has been successful in preclinical and clinical trials for the treatment of chronic lymphocytic leukemia and metastatic melanoma. Additionally, soluble B7 fusion proteins have demonstrated promising results in the immunotherapy of solid tumors as single agent immunotherapies (Lechner et al. (2011) Immunotherapy 3(11): 1317-1340; Dotti et al. (2002) Blood 100(1):200-207).

6. Modifications that Increase Uptake of Gram-Negative Bacteria, Such as Salmonella, by Immune Cells and Reduce Immune Cell Death

The genome of the immunostimulatory bacteria provided herein can be modified to increase or promote infection of immune cells, particularly immune cells in the tumor microenvironment, such as phagocytic cells. This includes reducing infection of non-immune cells, such as epithelial cells, or increasing infection of immune cells. The bacteria also can be modified to decrease pyroptosis in immune cells. Numerous modifications of the bacterial genome can do one or both of increasing infection of immune cells and decreasing pyroptosis. The immunostimulatory bacteria provided herein include such modifications, for example, deletions and/or disruptions of genes involved in the SPI-1 T3SS pathway, such as disruption or deletion of hilA, and/or disruption/deletion of genes encoding flagellin, rod protein and needle protein.

The invasive phenotype of Gram-negative bacteria, such as Salmonella, can result from the activity of genes encoded in pathways that promote the invasion of host cells. The invasion-associated Salmonella pathogenicity island-1 (SPI-1) of Salmonella is exemplary. SPI-1 includes the type 3 secretion system (T3SS), that is responsible for translocation of effector proteins into the cytosol of host cells. These proteins can cause actin rearrangements that lead to the uptake of Salmonella. T3SS effectors mediate the uptake of S. typhimurium into non-phagocytic host cells, such as epithelial cells. The SPI-1 T3SS has been shown to be essential for crossing the gut epithelial layer, but is dispensable for infection when bacteria are injected parenterally, for example. SPI-1 mutants have defects in epithelial cell invasion, dramatically reducing oral virulence, but are taken up normally by phagocytic cells, such as macrophages (Kong et al. (2012) Proc. Natl. Acad. Sci. U.S.A. 109(47):19414-19419). The immunostimulatory S. typhimurium strains provided herein can be engineered with mutations in SPI-1 T3SS genes, preventing their uptake by epithelial cells, and focusing them to immune cells such as macrophages, enhancing the anti-tumor immune response.

T3SS effectors also activate the NLRC4 inflammasome in macrophages, activating caspase-1 and leading to cell death via pyroptosis. Pyroptosis is a highly inflammatory form of programmed cell that occurs most frequently following infection with intracellular pathogens, and plays a role in the antimicrobial response. This pro-inflammatory cell death can limit the initiation of a robust adaptive immune response by directly inducing the death of antigen-presenting cells (APCs), as well as modifying the cytokine milieu to prevent the generation of memory T-cells. SPI-1 induces pyroptosis by injecting flagellin, needle and rod proteins (PrgI/J), while the extracellular flagellin stimulates TLR5 signaling. Thus, engineering the immunostimulatory bacteria herein to contain mutations in the genes involved in pyroptosis can enhance the anti-tumor immune effect by reducing cell death in immune cells such as macrophages.

Macrophage Pyroptosis

The macrophage NLRC4 inflammasome, which plays a role in the innate immune and antimicrobial responses, is a large multi-protein complex that recognizes cytosolic pathogens and provides for the autocatalytic activation of caspase-1. Activation of caspase-1 induces maturation and release of the pro-inflammatory cytokines IL-1β and IL-18, and triggers pyroptosis, a rapid inflammatory form of macrophage cell death. Infection by certain Gram-negative bacteria encoding type 3 or 4 secretion systems, such as Salmonella typhimurium and Pseudomonas aeruginosa, triggers the activation of the NLRC4 inflammasome upon recognition of bacterial ligands such as needle protein, rod protein and flagellin, following translocation into the host cell cytosol by the Stm pathogenicity island-1 type III secretion system (SPI-1 T3SS). Pyroptosis is not limited to macrophages; caspase-1-dependent death has been observed in dendritic cells following infection with Salmonella (Li et al. (2016) Scientific Reports 6:37447; Chen et al. (2014) Cell Reports 8:570-582; Fink and Cookson (2007) Cellular Microbiology 9(11):2562-2570). As shown herein, the knock-out of genes in the Salmonella genome involved in the induction of pyroptosis enhances the anti-tumor immune response. This prevents the loss of immune cells, including macrophages, following bacterial infection. For example, genes encoding hilA, rod protein (PrgJ), needle protein (PrgI), flagellin and/or QseC can be knocked out/disrupted in the immunostimulatory bacteria provided herein.

hilA

The invasion-associated Salmonella pathogenicity island-1 (SPI-1), including the type 3 secretion system (T3SS), is responsible for the translocation of effector proteins into the cytosol of host cells, causing actin rearrangements that lead to the uptake of Salmonella. hilA is a transcriptional activator for SPI-1 genes, and its expression is regulated by environmental signals such as, for example, oxygen, osmolarity, pH and growth phase. Suboptimal conditions repress the expression of hilA, thereby suppressing the invasive phenotype of the bacterium (Kong et al. (2012) Proc. Natl. Acad. Sci. U.S.A. 109(47):19414-19419). T3SS effectors mediate the uptake of S. typhimurium into non-phagocytic host cells, such as epithelial cells. The SPI-1 T3SS is essential for crossing the gut epithelial layer, but is dispensable for infection, such as when bacteria are injected parenterally. SPI-1 mutants have defects in epithelial cell invasion, reducing oral virulence, but are taken up normally by phagocytic cells, such as macrophages. The immunostimulatory bacteria provided herein include those with deletion or disruption of the hilA gene and/or other genes in the T3SS pathway. When these bacteria are administered, such as intravenously or intratumorally, infection is focused towards phagocytic cells, such as macrophages and dendritic cells, that do not require the SPI-1 T3SS for uptake. This enhances the safety profile of the immunostimulatory bacteria provided herein. It prevents off-target cell invasion and prevents fecal-oral transmission.

In addition to reducing the uptake of Salmonella by non-phagocytic cells, such as epithelial cells, deletion or disruption of hilA and/or other genes in this pathway also prolongs the longevity of the phagocytic cells, by preventing pyroptosis in macrophages, thus, inducing less cell death in human macrophages compared to bacteria that do not contain a deletion in hilA. For example, hilA deficient Salmonella strains prevent pyroptosis by preventing inflammasome activation, but maintain TLR5 signaling. hilA deletion/disruption also allows for the prolonged secretion of cytokines, such as those encoded by the immunostimulatory bacteria provided herein, and for macrophage trafficking to tumors, thus improving the efficacy of the immunostimulatory bacteria. For example, in comparison to S. typhimurium containing intact hilA, such as VNP20009, the hilA deletion mutants, exemplified herein, further reduce the quantity of pro-inflammatory cytokines, such as IL-6, increasing the tolerability of the therapy, as well as the quality of the adaptive immune response.

Flagellin

Bacterial, such as Salmonella, flagellin, in addition to SPI-1 T3SS, is necessary for triggering pyroptosis in macrophages, and can be detected by the macrophage NLRC4 inflammasome. Flagellin, which is the major component of flagellum, is recognized by TLR5. Salmonella encodes two flagellin genes, fliC and fljB; elimination of flagellin subunits decreases pyroptosis in macrophages. For example, S. typhimurium with deletions in fliC and fljB resulted in significantly reduced IL-1β secretion compared to the wild-type strain, whereas cellular uptake and intracellular replication of the bacterium remained unaffected. This demonstrates that flagellin plays a significant role in inflammasome activation. Additionally, S. typhimurium strains engineered to constitutively express FliC were found to induce macrophage pyroptosis (Li et al. (2016) Scientific Reports 6:37447; Fink and Cookson (2007) Cellular Microbiology 9(11):2562-2570; Winter et al. (2015) Infect. Immun. 83(4):1546-1555). The genome of the immunostimulatory bacteria herein can be modified to delete or mutate the flagellin genes fliC and fljB in S. typhimurium, leading to decreased cell death of tumor resident immune cells, such as macrophages, and enhancing the antitumor immune response of the immunostimulatory bacteria.

Rod Protein (PrgJ)

NLRC4 also detects aflagellated S. typhimurium. The flagellin-independent response was discovered to be due to the detection of PrgJ, which is the SPI-1 T3SS rod protein in S. typhimurium. Delivery of purified PrgJ protein to the macrophage cytosol resulted in rapid NLRC4-dependent caspase-1 activation, as well as secretion of IL-1β, similar to the effects induced by flagellin (Miao et al. (2010) Proc. Natl. Acad. Sci. U.S.A. 107(7):3076-3080). Thus, the mutation or knockout of the gene encoding PrgJ in S. typhimurium can reduce macrophage pyroptosis, which enhances the antitumor immune effect of the immunostimulatory bacteria, by preserving immune cells that are susceptible to being killed by the bacteria.

Needle Protein (PrgI)

PrgI, which is the SPI-1 T3SS needle protein in S. typhimurium, also is recognized by, and activates, NLRC4. The delivery of S. typhimurium PrgI to the cytosol of human primary monocyte-derived macrophages resulted in IL-1β secretion and subsequent cell death, while a Salmonella mutant that expresses PrgI but not flagellin was shown to activate the inflammasome in primary monocyte-derived macrophages at later time points than strains expressing flagellin (Kortmann et al. (2015) J. Immunol. 195:815-819). The immunostimulatory bacteria provided herein can be modified to mutate or delete the gene encoding needle protein in S. typhimurium, preventing immune cell pyroptosis, and enhancing the antitumor immune effect.

QseC

QseC is a highly conserved membrane histidine sensor kinase that is found in many Gram-negative bacteria, responds to the environment and regulates the expression of several virulence factors, including the flhDC gene that encodes the master regulator of flagellum biosynthesis in S. typhimurium; the sopB gene, which encodes a protein that plays a role in the invasion of non-phagocytic cells, the early maturation and regulation of trafficking of the Salmonella-containing vacuole (SCV), and the inhibition of SCV-lysosome fusion; and the sifA gene, which is required for SCV maintenance and membrane integrity. It has been shown that selective inhibition of QseC by LED209 inhibits bacterial virulence without suppressing S. typhimurium growth, by inhibiting the QseC-mediated activation of virulence-related gene expression (e.g., flhDC, sifA and sopB), and partially protects mice from death following infection with S. typhimurium or Francisella tularensis. QseC blockade was found to inhibit caspase-1 activation, IL-1β release, and S. typhimurium-induced pyroptosis of macrophages, by inhibiting excess inflammasome activation in the infected macrophages. Inhibition of QseC also suppressed flagellar gene expression and motility, and suppressed the invasion and replication capacities of S. typhimurium in epithelial cells (Li et al. (2016) Scientific Reports 6:37447). Thus, modification of the immunostimulatory bacteria herein, to mutate or knockout the gene encoding QseC, can enhance the antitumor immune response by focusing S. typhimurium infection to non-epithelial cells, and by reducing cell death in immune cells, such as by preventing pyroptosis in macrophages.

7. Bacterial Culture Conditions

Culture conditions for bacteria can influence their gene expression. It has been documented that S. typhimurium can induce rapid pro-inflammatory caspase-dependent cell death of macrophages, but not epithelial cells, within 30 to 60 min of infection by a mechanism involving the SPI-1 and its associated T3SS-1 (Lundberg et. al (1999) Journal of Bacteriology 181(11):3433-3437). It is now known that this cell death is mediated by activation of the inflammasome that subsequently activates caspase-1, which promotes the maturation and release of IL-1β and IL-18 and initiates a novel form of cell death called pyroptosis (Broz and Monack (2011) Immunol. Rev. 243(1): 174-190). This pyroptotic activity can be induced by using log phase bacteria, whereas stationary phase bacteria do not induce this rapid cell death in macrophages. The SPI-1 genes are induced during log phase growth. Thus, by harvesting S. typhimurium to be used therapeutically at stationary phase, rapid pyroptosis of macrophages can be prevented. Macrophages are important mediators of the innate immune system and they can act to secrete cytokines that are critical for establishing appropriate anti-tumor responses. In addition, limiting pro-inflammatory cytokines such as IL-1β and IL-18 secretion will improve the tolerability of administered S. typhimurium therapy. As provided herein, immunostimulatory S. typhimurium harvested at stationary phase will be used to induce anti-tumor responses.

E. BACTERIAL ATTENUATION AND COLONIZATION

1. Deletion of Flagellin (fliC⁻/FljB⁻)

Provided are immunostimulatory bacteria, such as the Salmonella species S. typhimurium, engineered to lack both flagellin subunits fliC and fljB, to reduce pro-inflammatory signaling. For example, as shown herein, a Salmonella strain lacking msbB, which results in reduced TNF-alpha induction, is combined with fliC and fljB knockouts. The resulting Salmonella strain has a combined reduction in TNF-alpha induction and reduction in TLR5 recognition. These modifications, msbB⁻, fliC⁻ and fljB⁻, can be combined with a bacterial plasmid, optionally containing CpGs, and also a cDNA expression cassette to provide expression of a therapeutic protein under the control of a eukaryotic promoter, such as for example, an immunostimulatory protein, such as a cytokine or chemokine, such as IL-2, and/or also inhibitory molecules, such as antibodies, including antibody fragments, such as nanobodies, and/or RNAi molecule(s), targeting an immune checkpoint, such as TREX1, PD-L1, VISTA, SIRP-alpha, TGF-beta, beta-catenin, CD47, VEGF, and combinations thereof. The resulting bacteria have reduced proinflammatory signaling, and robust anti-tumor activity.

For example, as exemplified herein, a fliC⁻ and fljB⁻ double mutant was constructed in the asd-deleted strain of S. typhimurium strain VNP20009 or in a wild-type Salmonella typhimurium, such as one having all of the identifying characteristics of the strain deposited under ATCC accession no. 14028. VNP20009, which is a derivative of ATCC 14028, was attenuated for virulence by disruption of purI/purM, and was also engineered to contain an msbB deletion that results in production of a lipid A subunit of LPS that is less toxigenic than wild-type lipid A. This results in reduced TNF-α production in the mouse model after intravenous administration, compared to strains with wild-type lipid A.

A fliC⁻ and fljB⁻ double mutant was constructed on a wild-type strain of S. typhimurium and also engineered to contain the asd, purI/purM and msbB deletions. The bacterium is optionally pagP⁻. The resulting strains are exemplary of strains that are attenuated for bacterial inflammation by modification of lipid A to reduce TLR2/4 signaling, and deletion of the flagellin subunits to reduce TLR5 recognition and inflammasome induction. Deletion of the flagellin subunits combined with modification of the LPS allows for greater tolerability in the host, and directs the immunostimulatory response towards production of immunostimulatory proteins. The delivery of RNA interference by the modified bacteria against desired targets in the TME elicits an anti-tumor response and promotes an adaptive immune response to the tumor.

2. Deletion of Genes in the LPS Biosynthetic Pathway

The LPS of Gram-negative bacteria is the major component of the outer leaflet of the bacterial membrane. It is composed of three major parts, lipid A, a nonrepeating core oligosaccharide, and the O antigen (or O polysaccharide). O antigen is the outermost portion on LPS and serves as a protective layer against bacterial permeability, however, the sugar composition of O antigen varies widely between strains. The lipid A and core oligosaccharide vary less, and are more typically conserved within strains of the same species. Lipid A is the portion of LPS that contains endotoxin activity. It is typically a disaccharide decorated with multiple fatty acids. These hydrophobic fatty acid chains anchor the LPS into the bacterial membrane, and the rest of the LPS projects from the cell surface. The lipid A domain is responsible for much of the toxicity of Gram-negative bacteria. Typically, LPS in the blood is recognized as a significant pathogen associated molecular pattern (PAMP), and induces a profound pro-inflammatory response. LPS is the ligand for a membrane-bound receptor complex comprising CD14, MD2 and TLR4. TLR4 is a transmembrane protein that can signal through the MyD88 and TRIF pathways to stimulate the NFκB pathway and result in the production of pro-inflammatory cytokines such as TNF-α and IL-1β, the result of which can be endotoxic shock, which can be fatal. LPS in the cytosol of mammalian cells can bind directly to the CARD domains of caspases 4, 5, and 11, leading to autoactivation and pyroptotic cell death (Hagar et al. (2015) Cell Research 25:149-150). The composition of lipid A and the toxigenicity of lipid A variants is well documented. For example, a monophosphorylated lipid A is much less inflammatory than lipid A with multiple phosphate groups. The number and length of the acyl chains on lipid A can also have a profound impact on the degree of toxicity. Canonical lipid A from E. coli has six acyl chains, and this hexa-acylation is potently toxic. S. typhimurium lipid A is similar to that of E. coli; it is a glucosamine disaccharide that carries four primary and two secondary hydroxyacyl chains (Raetz and Whitfield (2002) Annu. Rev. Biochem. 71:635-700). As described above, msbB⁻ mutants of S. typhimurium cannot undergo the terminal myristoylation of its LPS and produce predominantly penta-acylated lipid A that is significantly less toxic than hexa-acylated lipid A. The modification of lipid A with palmitate is catalyzed by palmitoyl transferase (PagP). Transcription of the pagP gene is under control of the PhoP/PhoQ system, which is activated by low concentrations of magnesium, e.g., inside the SCV. Thus, the acyl content of S. typhimurium is variable, and with wild-type bacteria, it can be hexa- or penta-acylated. The ability of S. typhimurium to palmitate its lipid A increases resistance to antimicrobial peptides that are secreted into phagolysozomes.

In wild-type S. typhimurium, expression of pagP results in a lipid A that is hepta-acylated. In an msbB⁻ mutant (in which the terminal acyl chain of the lipid A cannot be added), the induction of pagP results in a hexa-acylated LPS (Kong et al. (2011) Infection and Immunity 79(12):5027-5038). Hexa-acylated LPS has been shown to be the most pro-inflammatory. While other groups have sought to exploit this pro-inflammatory signal, for example, by deletion of pagP to allow only hexa-acylated LPS to be produced (Felgner et al. (2016) Gut Microbes 7(2): 171-177; Felgner et al. (2018) Oncoimmunology 7(2): e1382791), this can lead to poor tolerability, due to the TNF-α-mediated pro-inflammatory nature of the LPS and paradoxically less adaptive immunity (Kocijancic et al. (2017) Oncotarget 8(30):49988-50001). Exemplified herein, is a live attenuated strain of S. typhimurium that can only produce penta-acylated LPS, that contains a deletion of the msbB gene (that prevents the terminal myristoylation of lipid A, as described above), and is further modified by deletion of pagP (preventing palmitoylation). A strain modified to produce penta-acylated LPS will allow for lower levels of pro-inflammatory cytokines, improved stability in the blood and resistance to complement fixation, increased sensitivity to antimicrobial peptides, enhanced tolerability, and increased anti-tumor immunity when further modified to express heterologous immune-stimulatory proteins and/or interfering RNAs against immune checkpoints.

As provided herein, a pagP⁻ mutant was also constructed on an asd, msbB, purI/purM and fliC/fljB deleted strain of S. typhimurium VNP20009 or wild-type S. typhimurium. The resulting strains are exemplary of strains that are attenuated for bacterial inflammation by modification of lipid A to reduce TLR2/4 signaling, and deletion of the flagellin subunits to reduce TLR5 recognition and inflammasome induction, and deletion of pagP to produce penta-acylated LPS. Deletion of the flagellin subunits combined with modification of the LPS allows for greater tolerability in the host, and greater stability in the blood and resistance to complement fixation, providing for improved trafficking to the tumor site, in order to direct the immuno-stimulatory response towards production of any gene product, such as immune-stimulatory proteins and/or delivery of RNA interference against desired targets in the TME to elicit an anti-tumor response and promote an adaptive immune response to the tumor.

3. Colonization

VNP20009 is an attenuated S. typhimurium-based microbial cancer therapy that was developed for the treatment of cancer. VNP20009 is attenuated through deletion of the genes msbB and purI (purM). The purI deletion renders the microbe auxotrophic for purines or adenosine. Deletion of the msbB gene reduced the toxicity associated with lipopolysaccharide (LPS) by preventing the addition of a terminal myristyl group to the lipid A domain (Khan et al., (1998) Mol. Microbiol. 29:571-579).

There is a difference between mouse and humans in the ability of VNP20009 to colonize tumors. Systemic administration of VNP20009 resulted in colonization of mouse tumors; whereas systemic administration of VNP20009 in human patients resulted in very little colonization. It was shown that in mice, VNP20009 showed a high degree of tumor colonization after systemic administration (Clairmont et al., (2000) J Infect Dis. 181:1996-2002; and Bermudes et al. (2001) Biotechnol. Genet. Eng. Rev. 18:219-33). In a Phase 1 Study in advanced melanoma patients, however, very little VNP20009 was detected in human tumors after a 30-minute intravenous infusion (see Toso et al., (2002) J. Clin. Oncol. 20:142-52). Patients that entered into a follow-up study evaluating a longer, four-hour infusion of VNP20009, also demonstrated a lack of detectable VNP20009 after tumor biopsy (Heimann et al. (2003) J. Immunother. 26:179-180). Following intratumoral administration, colonization of a derivative of VNP20009 was detected (Nemunaitis et al. (2003) Cancer Gene Ther. 10:737-44). Direct intratumoral administration of VNP20009 to human tumors resulted in tumor colonization, indicating that human tumors can be colonized at a high level, and that the difference in tumor colonization between mice and humans occurs only after systemic administration.

It is shown herein (see, e.g., Example 25) that VNP20009 is inactivated by human complement, which leads to low tumor colonization. Strains that provide improved resistance to complement are provided. These strains contain modifications in the bacterial genome and also can carry a plasmid, typically in low or medium copy number, to encode genes to provide for replication (asd under the control of a eukaryotic promoter), and nucleic acid(s) encoding a therapeutic product(s), such as, but not limited to, RNAi, immunostimulatory protein, such as cytokines, and other such therapeutic genes, as described elsewhere herein. The table below summarizes the bacterial genotypes/modifications, their functional effects, and the effects/benefits.

Genotype/Modification Functional effect Effect/Benefit ΔpurI Purine/adenosine Tumor-specific enrichment auxotrophy Limited replication in healthy tissue ΔmsbB LPS surface coat Decreased TLR4 recognition modification Reduced cytokine profile Improved safety ΔFLG Flagella knockout Removes major inflammatory and immune-suppressive element Decreased TLR5 recognition Reduced cytokine profile Improved safety ΔpagP LPS surface coat Removes major inflammatory and modifications immune-suppressive element Decreased TLR4 recognition Reduced IL-6 profile Improved safety Δasd (in genome) Plasmid maintenance Improved plasmid delivery Plasmid maintenance plasmid Express gene Eukaryotic promoter limits expression products under to cells containing the plasmid control of host- Long term expression in the TME recognized promoter (i.e., asd encoded on plasmid under control of host-recognized promoter) Expression of therapeutic product(s)

Strains provided herein are ΔFLG and/or ΔpagP. Additionally, the strains are one or more of ΔpurI (ΔpurM), ΔmsbB, and Δasd (in the bacterial genome). The plasmid is modified to encode products under control of host-recognized promoters (e.g., eukaryotic promoters, such as RNA polymerase II promoters, including those from eukaryotes, and animal viruses). The plasmids can encode asd to permit replication in vivo, as well as nucleic acids with other beneficial functions and gene products as described elsewhere herein.

The immunostimulatory bacteria are derived from suitable bacterial strains. Bacterial strains can be attenuated strains, or strains that are attenuated by standard methods, or that, by virtue of the modifications provided herein, are attenuated in that their ability to colonize is limited primarily to immunoprivilaged tissues and organs, particularly immune and tumor cells, including solid tumors. Bacteria include, but are not limited to, for example, strains of Salmonella, Shigella, Listeria, E. coli, and Bifidobacteriae. For example, species include Shigella sonnei, Shigella flexneri, Shigella dysenteriae, Listeria monocytogenes, Salmonella typhi, Salmonella typhimurium, Salmonella gallinarum, and Salmonella enteritidis. Other suitable bacterial species include Rickettsia, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Vibrio, Bacillus, and Erysipelothrix. For example, Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia tsutsugamuchi, Rickettsia mooseri, Rickettsia sibirica, Bordetella bronchiseptica, Neisseria meningitidis, Neisseria gonorrhoeae, Aeromonas eucrenophila, Aeromonas salmonicida, Francisella tularensis, Corynebacterium pseudotuberculosis, Citrobacter freundii, Chlamydia pneumoniae, Haemophilus somnus, Brucella abortus, Mycobacterium intracellulare, Legionella pneumophila, Rhodococcus equi, Pseudomonas aeruginosa, Helicobacter mustelae, Vibrio cholerae, Bacillus subtilis, Erysipelothrix rhusiopathiae, Yersinia enterocolitica, Rochalimaea quintana, and Agrobacterium tumerfacium.

Exemplary of the immunostimulatory bacteria provided herein are species of Salmonella. Exemplary of bacteria for modification as described herein are wild-type strains of Salmonella, such as the strain that has all of the identifying characteristics of the strain deposited in the ATCC as accession #14028. Engineered strains of Salmonella typhimurium, such as strain YS1646 (ATCC Catalog #202165; also referred to as VNP20009, see, International Application Publication No. WO 99/13053,) that is engineered with plasmids to complement an asd gene knockout and antibiotic-free plasmid maintenance. The strains then are modified to delete the flagellin genes and/or to delete pagP. The strains also are rendered auxotrophic for purines, particularly adenosine, and are asd⁻ and msbB⁻. The asd gene can be provided on a plasmid for replication in the eukaryotic host. These deletions and plasmids are described elsewhere herein. Any of the nucleic acid encoding therapeutic products and immunostimulatory proteins and products, described elsewhere herein and/or known to those of skill in the art, can be included on the plasmid. The plasmid generally is present in low to medium copy number as described elsewhere herein. Therapeutic products include immunostimulatory proteins, such as cytokines, that promote an anti-tumor immune response in the tumor microenvironment and other such products described herein.

F. CONSTRUCTING EXEMPLARY PLASMIDS ENCODING THERAPEUTIC PROTEINS

The immunostimulatory bacteria provided herein are modified. They include modifications to the bacterial genome and to bacterial expression and host cell invasion, as discussed below, such as to improve or increase targeting to or accumulation in tumors, tumor-resident immune cells, and the tumor microenvironment, and also, to include plasmids that encode products that are expressed in the bacteria by including a bacterial promoter, or in the host by including an appropriate eukaryotic promoter and other regulatory regions as appropriate. It is shown herein that the immunostimulatory bacteria that are flagellin⁻ (fliC⁻/fljB⁻) and/or pagP⁻, and optionally hilA⁻, exhibit increased tumor colonization, and, thus, can overcome the previous problems encountered with VNP20009, which failed to adequately colonize tumors in humans. The clinical activity of VNP20009 was disappointing in part due to its poor ability to colonize human tumors (Nemunaitis et al. (2003) Cancer Gene Ther. 10(10):737-744; Toso et al. (2002) J. Clin. Oncol. 20(1): 142-152; Heimann et al. (2003) J. Immunother. 26(2): 179-180).

To introduce the plasmids, the bacteria are transformed using standard methods, such as electroporation, with purified DNA plasmids constructed with routine molecular biology tools and methods (DNA synthesis, PCR amplification, DNA restriction enzyme digestion and ligation of compatible cohesive end fragments with ligase). As discussed throughout, the plasmids encode one or more therapeutic products, including proteins, such as antibodies and fragments thereof, and immunostimulatory proteins, such as interleukins, under control of host-recognized promoters. The encoded immunostimulatory proteins stimulate the immune system, particularly in the tumor microenvironment. The antibodies, including antibody fragments and single chain antibodies, can inhibit immune checkpoints.

The plasmid can encode, for example, a therapeutic product or therapeutic protein that is one or more of GM-CSF, IL-2, IL-7, IL-12p70 (IL-12p40+IL-12p35), IL-15, IL-15/IL-15R alpha chain complex, IL-2 that has attenuated binding to IL-2Ra, IL-18, IL-36 gamma, CXCL9, CXCL10, CXCL11, CCL3, CCL4, CCL5, proteins that are involved in or that effect or potentiate recruitment/persistence of T cells, CD40, CD40 ligand, OX40, OX40 ligand, 4-1BB, 4-1BB ligand, members of the B7-CD28 family, a TGF-beta polypeptide antagonist, a CD47 antagonist, interferon-α, interferon-β, interferon-γ, or members of the tumor necrosis factor receptor (TNFR) superfamily.

The bacteria can encode other products on the plasmids, such as one or more short hairpin (sh) RNA construct(s), or other inhibitory RNA modalities, whose expression inhibits, suppresses or disrupts expression of targeted genes. The therapeutic products, such as the immunostimulatory proteins, antibodies, and RNAi, such as shRNA or microRNA constructs, are expressed under control of a eukaryotic promoter, such as an RNA polymerase (RNAP) II or III promoter. Typically, RNAPIII (also referred to as POLIII) promoters are constitutive, and RNAPII (also referred to as POLII) can be regulated. In some examples, the shRNAs target the gene TREX1, to inhibit its expression. In some embodiments the plasmids encode a plurality of therapeutic products. Where a plurality of products, such as RNAi's, are encoded, expression of each can be under control of different promoters, or the products can be encoded polycistronically.

The nucleic acids encoding the therapeutic products/proteins can be under the control of a eukaryotic promoter that is an RNA polymerase II promoter or an RNA polymerase III promoter. The RNA polymerase II promoter can be a viral promoter or a mammalian RNA polymerase II promoter. The viral promoter can be one selected from among well-known viral promoters. Exemplary of such are a cytomegalovirus (CMV) promoter, an SV40 promoter, an Epstein Barr virus (EBV) promoter, a herpes virus promoter, and an adenovirus promoter.

The therapeutic product can be under the control of a eukaryotic RNA polymerase II (RNAP II) promoter. Many such promoters are very well known. Exemplary of such promoters is an RNAPII promoter selected from among, for example, an elongation factor-1 (EF1) alpha promoter, a ubiquitin C (UBC) promoter, a phosphoglycerate kinase 1 promoter (PGK) promoter, a CAG promoter (which consists of: (C) the cytomegalovirus (CMV) early enhancer element, (A) the promoter, the first exon and the first intron of chicken beta-actin gene, and (G) the splice acceptor of the rabbit beta-globin gene), an EIF4a1 (eukaryotic initiation factor 4A) promoter, a CBA promoter (chicken beta actin), an MND promoter, a GAPDH promoter, and a CD68 promoter. MND is a synthetic promoter that contains the U3 region of a modified MoMuLV LTR with myeloproliferative sarcoma virus enhancer (murine leukemia virus-derived MND promoter (myeloproliferative sarcoma virus enhancer, negative control region deleted, dl587rev primer-binding site substituted; see, e.g., Li et al. (2010)J. Neurosci. Methods vol. 189:56-64).

As provided herein, bacterial strains, such as strains of Salmonella, including S. typhimurium, are modified or identified to be auxotrophic for adenosine in the tumor microenvironment, and/or the genome of the immunostimulatory bacterium is modified so that it preferentially infects tumor-resident immune cells and/or so that it induces less cell death in tumor-resident immune cells, and the bacteria are modified to carry plasmids encoding a therapeutic product, such as an immunostimulatory protein, an antibody or antibody fragment, such as an anti-tumor antibody or fragment thereof or anti-checkpoint antibody, and other products, such as RNAi.

1. Immunostimulatory Proteins

As discussed below, and elsewhere herein, provided are immunostimulatory bacteria that contain sequences of nucleotides that encode gene products, such as immunostimulatory proteins, to confer, increase, or enhance immune responses in the tumor microenvironment. These immunostimulatory bacteria are modified to preferentially infect tumors, including tumor-resident immune cells, and/or the genome of the immunostimulatory bacteria is modified so that they induce less cell death in tumor-resident immune cells, whereby the immunostimulatory bacteria accumulate in tumor cells to thereby deliver the immunostimulatory proteins to the targeted cells to stimulate the immune response against the tumor. The immunostimulatory bacteria can further encode a tumor antigen to enhance the response against the particular tumor. Any of the immunostimulatory bacteria provided herein and described above and below can be modified to encode an immunostimulatory protein. Generally, the immunostimulatory protein is under the control of an RNA polymerase II (RNAPII) promoter, and also is encoded in the plasmid for secretion, upon expression, into the tumor microenvironment. Any of the bacteria described herein for modification, such as any of the strains of Salmonella, Shigella, E. coli, Bifidobacteriae, Rickettsia, Vibrio, Listeria, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Cholera, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Bacillus, and Erysipelothrix, or an attenuated strain thereof or a modified strain thereof encode the immunostimulatory protein so that it is expressed in the infected subject's cells. The immunostimulatory bacteria include those that are modified, as described herein, to colonize, accumulate in, or to preferentially infect, tumors, tumor-resident immune cells and/or the TME.

As discussed in section D5, and elsewhere herein, the immunostimulatory bacteria can encode immunostimulatory proteins, such as cytokines, including chemokines, that enhance or stimulate or evoke an anti-tumor immune response, particularly when expressed in tumors, in the tumor microenvironment and/or in tumor-resident immune cells.

The immunostimulatory bacteria herein can be modified to encode an immunostimulatory protein that promotes or induces or enhances an anti-tumor response. The immunostimulatory protein can be encoded on a plasmid in the bacterium, under the control of a eukaryotic promoter, such as a promoter recognized by RNA polymerase II, for expression in a eukaryotic subject, particularly the subject for whom the immunostimulatory bacterium is to be administered, such as a human. The nucleic acid encoding the immunostimulatory protein can include, in addition to the eukaryotic promoter, other regulatory signals for expression or trafficking in the cells, such as for secretion or expression on the surface of a cell.

Immunostimulatory proteins are those that, in the appropriate environment, such as a tumor microenvironment (TME), can promote or participate in or enhance an anti-tumor response by the subject to whom the immunostimulatory bacterium is administered. Immunostimulatory proteins include, but are not limited to, cytokines, chemokines and co-stimulatory molecules. These include cytokines, such as, but not limited to, IL-2, IL-7, IL-12, IL-15, and IL-18; chemokines, such as, but not limited to, CCL3, CCL4, CCL5, CXCL9, CXCL10, and CXCL11; and/or co-stimulatory molecules, such as, but not limited to, CD40, CD40L, OX40, OX40L, 4-1BB, 4-1BBL, GM-CSF, members of the TNF/TNFR superfamily and members of the B7-CD28 family. Other such immunostimulatory proteins that are used for treatment of tumors or that can promote, enhance or otherwise increase or evoke an anti-tumor response, known to those of skill in the art, are contemplated for encoding in the immunostimulatory bacteria provided herein.

In some embodiments, the immunostimulatory bacteria herein are engineered to express cytokines to stimulate the immune system, including, but not limited to, IL-2, IL-7, IL-12 (IL-12p70 (IL12p40+IL-12p35)), IL-15 (and the IL-15:IL-15R alpha chain complex), and IL-18. Cytokines stimulate immune effector cells and stromal cells at the tumor site, and enhance tumor cell recognition by cytotoxic cells. In some embodiments, the immunostimulatory bacteria can be engineered to express chemokines, such as, for example, CCL3, CCL4, CCL5, CXCL9, CXCL10 and CXCL11. These modifications and bacteria encoding them are discussed above, and exemplified below.

2. Antibodies and Antibody Fragments

Provided are immunostimulatory bacteria that contain sequences of nucleotides that encode gene products, such as antibodies and antibody fragments, to confer, increase, or enhance anti-tumor immune responses. These include antibodies and antibody fragments that target immune checkpoints, such as CTLA-4, PD-1, PD-L1, CD47, or that target tumor antigens and tumor neoantigens, including those identified from the tumor of a subject to be treated, amongst others, and, for example, anti-IL-6 antibodies that modulate, particularly inhibit, immune suppression. The antibodies or fragments thereof, such as scFv and other single chain antibodies, such as camelids and nanobodies, can be encoded on a plasmid in the bacterium, under the control of eukaryotic regulatory sequences and signals, including a eukaryotic promoter, such as a promoter recognized by RNA polymerase II, for expression in a eukaryotic subject, particularly the subject for whom the immunostimulatory bacterium is to be administered, such as a human. The nucleic acid encoding the antibodies and antibody fragments can include, in addition to the eukaryotic promoter, other regulatory signals for expression and/or trafficking in the cells, such as for secretion or expression on the surface of a cell.

These immunostimulatory bacteria are those provided herein whose genomes are modified to preferentially infect tumors, including tumor-resident immune cells, and/or to eliminate infection of cells that are not target cells, and/or so that they induce less cell death in tumor-resident immune cells, whereby the immunostimulatory bacteria accumulate in tumor cells to thereby deliver the antibody or antibody fragment to the targeted cells to stimulate the immune response against the tumor. The immunostimulatory bacteria also or alternatively can encode a tumor antigen or neoantigen to enhance the response against the particular tumor. Any of the immunostimulatory bacteria provided herein and described above and below can be modified to encode an antibody or fragment thereof. Generally, the antibody or fragment thereof is under the control of an RNA polymerase II (RNAPII) promoter, and also is encoded in the plasmid for secretion, upon expression, into the tumor microenvironment. Any of the bacteria described herein for modification, such as any of the strains of Salmonella, Shigella, E. coli, Bifidobacteriae, Rickettsia, Vibrio, Listeria, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Cholera, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Bacillus, and Erysipelothrix, or an attenuated strain thereof or a modified strain thereof encode the antibody or fragment thereof so that it is expressed in the infected subject's cells. The immunostimulatory bacteria include those that are modified, as described herein, to colonize, accumulate in, or to preferentially infect, tumors, tumor-resident immune cells and/or the tumor microenvironment.

Therapeutic antibodies and fragments thereof are well known. For example, there are a plethora of anti-CTLA4, anti-PD-1 and anti-PD-L1 antibodies and antigen-binding fragments thereof, such as Fab, Fab′, F(ab′)₂, single-chain Fv (scFv), Fv, disulfide-stabilized Fv (dsFv), nanobodies and camelids, and diabody fragments, single-chain antibodies, and humanized and human antibodies that are known. For example, antibodies that bind to PD-1 or PD-L1 and inhibit PD-1-inhibitory activity, and that have been used in anti-tumor immunotherapy are known. Exemplary anti-PD-1 antibodies include, but are not limited to, any of those described in U.S. Pat. Nos. 7,943,743, 8,008,449, and 8,735,553; U.S. Publication Nos. 2005/0180969 and 2007/0166281; and International Patent Application Publication No. WO 2008/156712. Anti-PD-L1 antibodies include, but are not limited to, any of those described in U.S. Publ. Nos. 2013/0034559 and 2013/0045202; U.S. Pat. Nos. 7,943,743, 8,217,149, 8,679,767, and 8,779,108; and Intl. App. Publ. Nos. WO 2010/077634 and WO 2013/019906. Several antibodies, which bind to and inhibit CTLA-4 activity, have been described, and have been used in anti-tumor immunotherapy. Anti-CTLA4 antibodies include, but are not limited to, any of those described in U.S. Pat. Nos. 6,682,736 and 6,984,720; U.S. Publ. Nos. 2002/0086014 and 2009/0074787; European Patent No. EP 1262193; and International Patent Application Publication No. WO 2000/037504. Anti-CTLA4 antibodies include Ipilimumab (also called MDX-010 or 10D1) and Tremelimumab (also called Ticilimumab or CP-675,206). These anti-CTLA4 antibodies have been involved in numerous clinical trials for the treatment of cancers. Ipilimumab is FDA approved for the treatment of melanoma and has been in clinical trials for other cancers, such as prostate cancer, lung cancer, and renal cell carcinoma (RCC). Tremelimumab has been investigated in clinical trials for the treatment of colorectal cancer (CRC), gastric cancer, melanoma and non-small cell lung cancer (NSCLC). Exemplary checkpoint inhibitors include, but are not limited to, anti-CTLA4 agents, anti-PD-1 agents, anti-PD-L1 agents and others, exemplary of which are the following:

Exemplary immune checkpoint target proteins and inhibitors Target Antibody/fusion Target Function protein Synonyms and Code Names CTLA4 Inhibitory Ipilimumab (MDX-CTLA-4; BMS-734016; MDX-010) receptor Tremelimumab (Ticilimumab; CP-675, 206) PD-1 Inhibitory MK-3475 (Pembrolizumab; Lambrolizumab; SCH 900475) receptor AMP-224 (anti-PD-1 fusion protein AMP-224) Nivolumab (BMS-936558; MDX-1106; ONO-4538) Pidilizumab (CT-011) PD-L1 Ligand for MDX-1105 (RG7446) PD-1 BMS-936559 MED14736 MPDL33280A

The immunostimulatory bacteria provided herein can be engineered to express any antibody/antigen-binding fragment thereof, including, but not limited to the anti-checkpoint antibodies (checkpoint antagonists/inhibitors) described herein, and known to those of skill in the art.

3. Interfering RNAs (RNAi)

The plasmids in the immunostimulatory bacterial strains herein encode the RNAi nucleic acids targeting the immune checkpoints and other targets of interest, as described above. RNAi includes shRNA, siRNA, and microRNA. RNA interference (RNAi) allows for the sequence-selective suppression of gene expression in eukaryotic cells using small interfering RNAs (siRNAs), which are short, synthetic, dsRNA molecules with a sequence homologous to the target gene. RNAi technology provides a powerful tool for the depletion of disease-related transcripts.

a. shRNA

The siRNAs, which are typically about 19-29 base pairs long, function by degrading specific host mRNA sequences, precluding translation into their respective protein products, effectively silencing the expression of the target gene. Short hairpin RNAs (shRNAs), containing a tight hairpin loop, are widely used in RNAi. shRNAs contain of two complementary RNA sequences, each 19-29 bps long, linked by a loop spacer of 4-15 nucleotides. The RNA sequence that is complementary to the target gene sequence (and is thus identical to the mRNA sequence), is known as the “sense” strand, while the strand which is complementary to the mRNA (and identical to the target gene sequence) is known as the “antisense” or “guide” strand. shRNA transcripts are processed by an RNase III enzyme known as Dicer into siRNA duplexes. The product is then loaded into the RNA-induced silencing complex (RISC) with Argonaute (Ago) proteins and other RNA-binding proteins. RISC then localizes the antisense, or “guide” strand to its complimentary mRNA sequence, which is subsequently cleaved by Ago (U.S. Pat. No. 9,624,494). The use of shRNA is preferred over siRNA, because it is more cost effective, high intracellular concentrations of siRNA are associated with off-target effects, and because the concentration of siRNA becomes diluted upon cell division. The use of shRNA, on the other hand, results in stable, long-term gene knockdown, without the need for multiple rounds of transfection (Moore et al. (2010) Methods Mol. Bio. 629:141-158).

Targets of interest for RNAi, such as micro-RNA and siRNA/shRNA-mediated silencing include, but are not limited to, developmental genes such as cytokines and their receptors, cyclin kinase inhibitors, neurotransmitters and their receptors, growth/differentiation factors and their receptors; oncogenes such as BCL2, ERBA, ERBB, JUN, KRAS, MYB, MYC; tumor suppressor genes such as BRCA1, BRCA2, MCC, p53; and enzymes such as ACC synthases and oxidases, ATPases, alcohol dehydrogenases, amylases, catalases, DNA polymerases, RNA polymerases, kinases, lactases and lipases (U.S. Pat. Nos. 7,732,417, 8,829,254, 8,383,599, 8,426,675, 9,624,494; U.S. Patent Publication No. 2012/0009153). Of particular interest are immune checkpoint targets, such as PD-1, PD-2, PD-L1, PD-L2, CTLA-4, IDO 1 and 2, CTNNB1 (β-catenin), SIRPα, VISTA, RNase H2, DNase II, CLEVER-1/Stabilin-1, LIGHT, HVEM, LAG3, TIM3, TIGIT, Galectin-9, KIR, GITR, TIM1, TIM4, CEACAM1, CD27, CD47, CD40, CD40L, CD48, CD70, CD80, CD86, CD112, CD137(4-1BB), CD155, CD160, CD200, CD226, CD244 (2B4), CD272 (BTLA), B7-H2, B7-H3, B7-H4, B7-H6, ICOS, A2aR, A2bR, HHLA2, ILT-2, ILT-4, gp49B, PIR-B, HLA-G, ILT-2/4, OX40 and OX-40L. Other targets include MDR1, Arginase1, iNOs, IL-10, TGF-β, pGE2, STAT3, VEGF, VEGFR, KSP, HER2, Ras, EZH2, NIPP1, PP1, TAK1 and PLK1 (U.S. Patent Publication Nos. 2008/091375, 2009/0208534, 2014/0186401, 2016/0184456, 2016/0369282; International Application Publication Nos. WO 2012/149364, WO 2015/002969, WO 2015/032165, WO 2016/025582).

Expressed RNAi, such as shRNAs, mediate long-term, stable knockdown of their target transcripts for as long as the shRNAs are transcribed. RNA Pol II and III promoters are used to drive expression of shRNA constructs, depending on the type of expression required. Consistent with their normal cellular roles in producing abundant, endogenous small RNAs, Pol III promoters (such as U6 or H1) drive high levels of constitutive shRNA expression, and their transcription initiation points and termination signals (4-6 thymidines) are well defined. Pol II promoter-driven shRNAs can be expressed tissue-specifically and are transcribed as longer precursors that mimic pri-miRNAs and have cap and polyA signals that must be processed. Such artificial miRNAs/shRNAs are efficiently incorporated into RISC, contributing to a more potent inhibition of target-gene expression; this allows lower levels of shRNA expression and might prevent saturation of components in the RNAi pathway. An additional advantage of Pol II promoters is that a single transcript can simultaneously express several miRNA and mimic shRNAs. This multiplexing strategy can be used to simultaneously knock down the expression of two or more therapeutic targets, or to target several sites in a single gene product (see, e.g., U.S. Publication No. 2009/0208534).

b. MicroRNA

MicroRNAs (miRNAs) are short, non-coding single-stranded RNA molecules that are about or are 20-24 nucleotides long. Naturally-occurring miRNAs are involved in the post-transcriptional regulation of gene expression; miRNAs do not encode genes. miRNAs have been shown to regulate cell proliferation and survival, as well as cellular differentiation. miRNAs inhibit translation or promote RNA degradation by binding to target mRNAs that share sequence complementarity. They affect the stability and translation of mRNAs; miRNAs inhibit translation, and/or promote RNA degradation, by binding to target mRNAs that share sequence complementarity. miRNAs, which occur in eukaryotes, are transcribed by RNA Pol II into capped and polyadenylated hairpin-containing primary transcripts, known as primary miRNAs, or pri-miRNAs. These pri-miRNAs are cleaved by the enzyme Drosha ribonuclease III and its cofactor Pasha/DGCR8 into ˜70 nucleotide long precursor miRNA hairpins, known as precursor miRNAs, or pre-miRNAs, which are then transported from the nucleus into the cytoplasm, and cleaved by Dicer ribonuclease III into the miRNA: miRNA* duplex, with sense and antisense strand products that are approximately 22 nucleotides long. The mature miRNA is incorporated into the RNA-induced silencing complex (RISC), which recognizes and binds target mRNAs, usually at the 3′-untranslated region (UTR), through imperfect base pairing with the miRNA, resulting in the inhibition of translation, or destabilization/degradation of the target mRNA (see, e.g., Auyeung et al. (2013) Cell 152(4):844-85).

As described herein, regulating gene expression by RNA interference (RNAi), often uses short hairpin RNAs (shRNAs) to inhibit, disrupt or other interfere with expression of targeted genes. While advantageously used, and used herein, in some instances, shRNAs can be poor substrates for small RNA biogenesis factors, they can be processed into a heterogeneous mix of small RNAs, and their precursor transcripts can accumulate in cells, resulting in the induction of sequence-independent, non-specific effects and leading to in vivo toxicity. miRNAs are contemplated for use herein. miRNA-like scaffolds, or artificial miRNAs (amiRNAs) can be used to reduce sequence-independent non-specific effects (Watanabe et al. (2016) RNA Biology 13(1):25-33; Fellmann et al. (2013) Cell Reports 5:1704-1713). In addition to improved safety profiles, amiRNAs are more readily transcribed by Pol II than shRNAs, allowing for regulated and cell-specific expression. Artificial miRNAs (amiRNAs), in comparison to shRNAs, can effectively, and in some cases, more potently, silence gene expression without generating large amounts of inhibitory RNAs (McBride et al. (2008) Proc. Natl. Acad. Sci. U.S.A. 105(15):5868-5873). This effect was determined to be due to the more effective processing of siRNA from pre-miRNA precursors than from shRNA transcripts (Boden et al. (2004) Nucl. Acid Res. 32(3):1154-1158).

miRNAs have been shown to regulate several cellular processes, including cell proliferation and survival, intracellular signaling, cellular metabolism, and cellular differentiation. In 1993, the first miRNA was identified in C. elegans (Lee et al. (1993) Cell 75:843-854), and later, mammalian miRNAs were identified (Pasquinelli et al. (2000) Nature 408(6808):86-89). More than 17,000 miRNAs in 142 species have been identified, with more than 1900 miRNAs identified in humans, many of which have been associated with a variety of diseases, including cancer (e.g., miR-15 and miR-16 in B-CLL, miR-125b, miR-145, miR-21, miR-155 and miR-210 in breast cancer, miR-155 and let-7a in lung cancer, miR-145 in gastric cancer, miR-29b in liver cancer); viral infections (e.g., miR-122 and miR-155 in HCV infection, mir-28, miR-125b, miR-150, miR-223 and miR-382 in HIV-1 infection, miR-21 and miR-223 in influenza virus infection); immune-related diseases (e.g., miR-145, miR-34a, miR-155 and miR-326 in multiple sclerosis, miR-146a in systemic lupus erythematosus, miR-144, miR-146a, miR-150, miR-182, miR-103 and miR-107 in type II diabetes, miR-200a, miR-200b, miR-429, miR-122, miR-451 and miR-27 in nonalcoholic fatty liver disease, miR-29c, miR-34a, miR-155 and miR-200b in non-alcoholic steatohepatitis); and neurodegenerative diseases (e.g., miR-30b, miR-30c, miR-26a, miR-133b, miR-184* and let-7 in Parkinson's disease, miR-29b-1, miR-29a and miR-9 in Alzheimer's disease) (Li and Kowdley (2012) Genomics Proteomics Bioinformatics 10:246-253).

Studies have shown that specific endogenous miRNAs are up-regulated or down-regulated in certain cancers. For example, miR-140 is down-regulated in non-small cell lung cancer (NSCLC) and its overexpression was found to suppress PD-L1 (Xie et al. (2018) Cell Physiol. Biochem. 46:654-663); miR-197 is downregulated in platinum-based chemotherapy resistant NSCLC, resulting in chemoresistance, tumorigenicity and metastasis (Fujita et al. (2015) Mol. Ther. 23(4):717-727); and several miRNAs have been found to be down-regulated in cancer cells to allow PD-L1 expression, including miR-200, miR-34a and miR-138 (Yee et al. (2017) J. Biol. Chem. 292(50):20683-20693). Several miRNAs also are upregulated, for example miR-21, miR-17 and miR-221 in lung cancer (Xie et al. (2018) Cell Physiol. Biochem. 46:654-663).

MicroRNA-103 (miR-103) was identified as the most upregulated microRNA in endothelial cells as a result of genotoxic stress and DNA damage following radiation. It was found that miR-103 led to the downregulation of the TREX1, TREX2 and FANCF genes, and the decrease in TREX1 expression was identified as the major mechanism by which miR-103 mediates cell death and suppresses angiogenesis (Wilson et al. (2016) Nature Communications 7:13597). Since the loss of TREX1 results in the accumulation of dsDNA and ssDNA, defective DNA repair, and release of cytokines, miR-103 expression significantly upregulates the pro-inflammatory chemokines IP-10, RANTES, MIG, and the cytokines IL-15, IL-12 and IFN-γ, and this upregulation was due to a miR-103 mediated decrease in TREX1 levels. Studies also revealed a significant increase in costimulatory receptors CD40 and CD160, and a decrease in the numbers of PD-L1⁺ macrophages and neutrophils in the 4T1 tumors. miR-103 regulation of TREX1 is therefore a potent modulator of the immune TME. Other miRNAs that target TREX1 include miR-107 (U.S. Pat. No. 9,242,000), miR-27a and miR-148b (U.S. Pat. No. 8,580,757). miRNA-103 can be used in the plasmids herein to inhibit TREX1.

Artificial miRNAs (amiRNAs) can be delivered to cells and used to silence target genes by creating a microRNA-based siRNA or shRNA vector (shRNAmir). The miR-30a backbone is often used in mammals, and approximately 200-300 bases of the primary miRNA transcript are included in the vector, with the miRNA hairpin placed at the center of the fragment, and the natural miRNA stem sequence being replaced with the siRNA/shRNA-encoding sequence of interest. Viral promoters, such as CMV, MSCV and TLR promoters; cellular promoters, such as EIF-1a; inducible chimeric promoters, such as tet-CMV; and tissue-specific promoters, can be used (Chang et al. (2013) Cold Spring Harb. Protoc.; doi:10.1101/pdb.prot075853). Other miRNAs that can be used include mir-16-2 (Watanabe et al. (2016) RNA Biology 13(1):25-33), miR-155 (Chung et al. (2006) Nuc. Acids Res. 34:e53), miR17-92 (Liu et al. (2008) Nuc. Acids Res. 36(9):2811-2824), miR-15a, miR-16, miR-19b, miR-20, miR-23a, miR-27b, miR-29a, miR-30b, miR-30c, miR-104, miR-132s, miR-181, miR-191, miR-223 (U.S. Pat. No. 8,426,675), and Let-7 miRNA (WO 2009/006450; WO 2015/032165).

shRNAmirs are limited by the low effectiveness of computationally-predicted shRNA sequences, particularly when expressed under low or single copy conditions. Third generation artificial miRNAs, such as miR-E (based on miR-30a) and miR-3G (based on miR-16-2) have been developed, and were found to exhibit stronger gene silencing in both Pol II- and Pol III-based expression vectors in comparison to shRNAmirs, due to the enhanced processing and accumulation of precisely-defined guide RNAs. miR-E, which was developed by the discovery of the conserved CNNC motif that enhances the processing of miRNA within the stem 3p flanking sequences, is different from endogenous miR-30a in three aspects: the stem of miR-E has no bulge and has the intended guide on the opposite strand; two conserved base pairs flanking the loop were mutated from CU/GG to UA/UA; and XhoI/EcoRI restriction sites were introduced into the flanking regions for shRNA cloning (Fellmann et al. (2013) Cell Reports 5:1704-1713). miR-E was found to be more potent than miR-30a, but symmetric processing of both the 3p and 5p strands of miR-30a does not favor guide strand delivery over passenger strand delivery, which is not optimal. Additionally, cloning into miR-E using oligos longer than 100 nt is costly and time consuming (Watanabe et al. (2016) RNA Biology 13(1):25-33).

The amiRNA designated miR-16-2 (see, e.g., Watanabe et al. (2016) RNA Biology 13(1):25-33, see FIG. 1 ) is a third generation (3G) amiRNA scaffold alternative; it is expressed in several tissues, is naturally asymmetric (the mature strand is derived exclusively from the 5p or 3p arm of the stem), and its stem and loop segments are small and rigid, simplifying vector cloning. miR-3G is generated by cloning the ˜175 bp fragment containing the native miR-16-2 stem and loop, and the flanking 35 bps on either side of the stem, into the vector. miR-3G includes further modification of miR-16-2 by introducing cloning sites, such as MluI and EcoRI, into the 5p and 3p arm-flanking sequences, respectively, and fully base-pairing the guide (antisense) and passenger (sense) strand stem, with the exception of a mismatch at position 1 relative to the guide strand. The restriction sites allow for the generation of new targeting constructs via 88-mer duplexed DNA oligonucleotides without compromising the predicted secondary structure of the miR-16-2 hairpin and flanking elements. Additionally, one of the two CNNC motifs and the GHG motif (small RNA processing enhancers) are modified in the 3p flanking sequence of miR-16-2. siRNAs targeting the gene(s) of interest are then exchanged with the first 21 nucleotides of the mature 5p guide and 3p passenger sequences. Studies determined that miR-E and miR-3G were equally potent. miR-3G provides an attractive RNAi system, due to the smaller size of its expression cassette (˜175 nts vs. ˜375 for miR-E), and the simplified and cost effective single step cloning method for its production. As with shRNAs, bacteria can be used as vectors for the in vivo delivery of micro-RNAs. For example, it was shown that attenuated S. typhimurium can be used as a vector for the oral delivery of plasmids expressing miRNA against CCL22 in mice with inflammation. Downregulation of CCL22 gene expression by this method was successful both in vitro and in vivo in mouse models of atopic dermatitis (Yoon et al. (2012) DNA and Cell Biology 31(3):289-296). For purposes herein a miRNA 16-2 can be used to produce miRNAs to be used in place of the shRNA. The sequences for the shRNA can be used for design of miRNAs.

DNA encoding RNAi for disrupting and/or inhibiting and/or targeting any of selected target genes, such as any immune checkpoint described herein or known to the skilled artisan, is inserted into a microRNA backbone, such as the microRNA backbone set forth in SEQ ID NO:249, and below. Any suitable microRNA backbone known to the skilled artisan can be used; generally such backbones are based on a naturally-occurring microRNA and are modified for expression of the RNAi. Exemplary of such backbones is one based on miR-16-2 (SEQ ID NO:248). The sequence of the modified microRNA backbone is:

(SEQ ID NO: 249) 5′-CCGGATCAACGCCCTAGGTTTATGTTTGGATGAACTGACATACGCGT ATCCGTCNNNNNNNNNNNNNNNNNNNNNGTAGTGAAATATATATTAAACN NNNNNNNNNNNNNNNNNNNNTACGGTAACGCGGAATTCGCAACTATTTTA TCAATTTTTTGCGTCGAC-3′, where the N's represent complementary, generally 18-26, such as 19-24, 19-22, 19-20, base pair long anti-sense and sense nucleotide sequences that target the gene to be silenced, and are inserted before and after the microRNA loop. RNAs, such as ARI-205 (SEQ ID NO:214) and ARI-206 (SEQ ID NO:215) are exemplary constructs based on the microRNA backbone of SEQ ID NO:249, that encode 21 and 22 base pair homology sequences, respectively. ARI-207 (SEQ ID NO:216) and ARI-208 (SEQ ID NO:217) are exemplary constructs based on the microRNA backbone of SEQ ID NO:249, that encode 19 base pair homology sequences. Another example, is the construct designated ARI-201, which is microRNA construct ARI-205, wherein the N's are replaced with a sequence of nucleotides targeting mouse PD-L1. The construct designated ARI-202 represents microRNA construct ARI-206, where the N's are replaced with sequences targeting mouse PD-L1. The skilled person readily can construct microRNAs for inclusion in plasmids as described and exemplified herein using the miR-16-2 backbone, or other suitable backbones known to the skilled artisan.

4. Origin of Replication and Plasmid Copy Number

Plasmids are autonomously-replicating extra-chromosomal circular double stranded DNA molecules that are maintained within bacteria by means of a replication origin. Copy number influences the plasmid stability. High copy number generally results in greater stability of the plasmid when the random partitioning occurs at cell division. A high number of plasmids generally decreases the growth rate, thus possibly allowing for cells with few plasmids to dominate the culture, since they grow faster. The origin of replication also determines the plasmid's compatibility: its ability to replicate in conjunction with another plasmid within the same bacterial cell. Plasmids that utilize the same replication system cannot co-exist in the same bacterial cell. They are said to belong to the same compatibility group. The introduction of a new origin, in the form of a second plasmid from the same compatibility group, mimics the result of replication of the resident plasmid. Thus, any further replication is prevented until after the two plasmids have been segregated to different cells to create the correct pre-replication copy number.

Origin Copy SEQ ID of Replication Number NO. pMB1 15-20 254 p15A 10-12 255 pSC101 ~5 256 pBR322 15-20 243 ColE1 15-20 257 pPS10 15-20 258 RK2 ~5 259 R6K (alpha origin) 15-20 260 R6K (beta origin) 15-20 261 R6K (gamma\origin) 15-20 262 P1 (oriR) Low 263 R1 Low 264 pWSK Low 265 ColE2 10-15 266 pUC (pMB1) 500-700 267 F1 300-500 268

Numerous bacterial origins of replication are known to those of skill in the art. The origin can be selected to achieve a desired copy number. Origins of replication contain sequences that are recognized as initiation sites of plasmid replication via DNA dependent DNA polymerases (Solar et al. (1998) Microbiology And Molecular Biology Reviews 62(2):434-464). Different origins of replication provide for varying plasmid copy levels within each cell and can range from 1 to hundreds of copies per cell. Commonly used bacterial plasmid origins of replication include, but are not limited to, pMB1 derived origins, which have very high copy derivatives, ColE1 origins, p15A, pSC101, pBR322, and others, which have low copy numbers. Such origins are well known to those of skill in the art. The pUC19 origin results in copy number of 500-700 copies per cell. The pBR322 origin has a known copy number of 15-20. These origins only vary by a single base pair. The ColE1 origin copy number is 15-20, and derivatives such as pBluescript have copy numbers ranging from 300-500. The p15A origin that is in pACYC184, for example, results in a copy number of approximately 10. The pSC101 origins confer a copy number of approximately 5. Other low copy number vectors from which origins can be obtained, include, for example, pWSK29, pWKS30, pWKS129 and pWKS130 (see, Wang et al. (1991) Gene 100:195-199). Medium to low copy number is less than 150, or less than 100. Low copy number is less than 20, 25, or 30. Those of skill in the art can identify plasmids with low or high copy number. For example, one way to determine experimentally if the copy number is high or low is to perform a miniprep. A high-copy plasmid should yield between 3-5 μg DNA per 1 ml LB culture; a low-copy plasmid will yield between 0.2-1 μg DNA per ml of LB culture.

Sequences of bacterial plasmids, including identification of and sequence of the origin of replication, are well known (see, e.g., snapgene.com/resources/plasmid_files/basic_cloning_vectors/pBR322/).

High copy plasmids are selected for heterologous expression of proteins in vitro because the gene dosage is increased relative to chromosomal genes and higher specific yields of protein, and for therapeutic bacteria, higher therapeutic dosages of encoded therapeutics. It is shown, herein, however, that for delivery of plasmids encoding RNA interference (RNAi), such as by S. typhimurium, as described herein, while it would appear that a high copy plasmid would be ideally suited, therapeutically, a lower copy number is more effective.

The requirement for bacteria to maintain the high copy plasmids can be a problem if the expressed molecule is toxic to the organism. The metabolic requirements for maintaining these plasmids can come at a cost of replicative fitness in vivo. Optimal plasmid copy number for delivery of interfering RNAs can depend on the mechanism of attenuation of the strain engineered to deliver the plasmid. If needed, the skilled person, in view of the disclosure herein, can select an appropriate copy number for a particular immunostimulatory species and strain of bacteria. It is shown herein, that low copy number can be advantageous.

5. CpG Motifs and CpG Islands

Unmethylated cytidine-phosphate-guanosine (CpG) motifs are prevalent in bacterial, but not vertebrate, genomic DNA. Pathogenic DNA and synthetic oligodeoxynucleotides (ODN) containing CpG motifs activate host defense mechanisms, leading to innate and acquired immune responses. The unmethylated CpG motifs contain a central unmethylated CG dinucleotide plus flanking regions. In humans, four distinct classes of CpG ODN have been identified based on differences in structure and the nature of the immune response they induce. K-type ODNs (also referred to as B-type) contain from 1 to 5 CpG motifs typically on a phosphorothioate backbone. D-type ODNs (also referred to as A-type) have a mixed phosphodiester/phosphorothioate backbone and have a single CpG motif, flanked by palindromic sequences that permits the formation of a stem-loop structure, as well as poly G motifs at the 3′ and 5′ ends. C-type ODNs have a phosphorothioate backbone and contain multiple palindromic CpG motifs that can form stem loop structures or dimers. P-Class CpG ODN have a phosphorothioate backbone and contain multiple CpG motifs with double palindromes that can form hairpins at their GC-rich 3′ ends (Scheiermann and Klinman (2014) Vaccine 32(48):6377-6389). For purposes herein, the CpGs are encoded in the plasmid DNA; they can be introduced as a motif, or in a gene.

Toll-like receptors (TLRs) are key receptors for sensing pathogen-associated molecular patterns (PAMPs) and activating innate immunity against pathogens (Akira et al. (2001) Nat. Immunol. 2(8):675-680). TLR9 recognizes hypomethylated CpG motifs in DNA of prokaryotes that do not occur naturally in mammalian DNA (McKelvey et al. (2011) J. Autoimmunity 36:76-86). Recognition of CpG motifs upon phagocytosis of pathogens into endosomes in immune cell subsets induces IRF7-dependent type I interferon signaling and activates innate and adaptive immunity.

Immunostimulatory bacteria, such as Salmonella species, such as S. typhimurium, strains carrying plasmids containing CpG islands, are provided herein. These bacteria can activate TLR9 and induce type I IFN-mediated innate and adaptive immunity. As exemplified herein, bacterial plasmids that contain hypomethylated CpG islands can elicit innate and adaptive anti-tumor immune responses that, in combination with RNAi encoded in the plasmid, such as RNAi that targets immune checkpoints, such as the shRNA or miRNA that targets TREX1, and hence, TREX1-mediated STING pathway activation, can have synergistic or enhanced anti-tumor activity. For example, the asd gene (SEQ ID NO:48) encodes a high frequency of hypomethylated CpG islands. CpG motifs can be included in combination with any of the RNAi described or apparent from the description herein in the immunostimulatory bacteria, and thereby enhance or improve anti-tumor immune responses in a treated subject.

Immunostimulatory CpGs can be included in the plasmids, by including a nucleic acid, typically from a bacterial gene, that encodes a gene product, and also by adding a nucleic acid that encodes CpG motifs. The plasmids herein can include CpG motifs. Exemplary CpG motifs are known (see, e.g., U.S. Pat. Nos. 8,232,259, 8,426,375 and 8,241,844). These include, for example, synthetic immunostimulatory oligonucleotides, between 10 and 100, 10 and 20, 10 and 30, 10 and 40, 10 and 50, 10 and 75, base pairs long, with the general formula: (CpG)_(n), where n is the number of repeats. Generally, at least one or two repeats are used; non-CG bases can be interspersed. Those of skill in the art are very familiar with the general use of CpG motifs for inducing an immune response by modulating TLRs, particularly TLR9.

6. Plasmid Maintenance/Selection Components

The maintenance of plasmids in laboratory settings is usually ensured by the inclusion of an antibiotic resistance gene on the plasmid and use of antibiotics in the growth media. As described above, the use of an asd deletion mutant complimented with a functional asd gene on the plasmid allows for plasmid selection in vitro without the use of antibiotics, and allows for plasmid maintenance in vivo. The asd gene complementation system provides for such selection/maintenance (Galán et al. (1990) Gene 28:29-35). The use of the asd gene complementation system to maintain plasmids in the tumor microenvironment increases the potency of S. typhimurium and other immunostimulatory bacterial strains, engineered to deliver plasmids encoding therapeutic products such as immunostimulatory proteins, antibodies, antibody fragments, or interfering RNAs.

7. RNA Polymerase Promoters

Plasmids provided herein are designed to encode interfering RNAs targeting immune checkpoints and other targets as described above. The RNA expression cassette contains a promoter for transcription in human cells such as an H1 promoter or a U6 promoter, or a CMV promoter. U6 and H1 are RNA polymerase III (RNAP III) promoters, which are for production and processing of small RNAs. The CMV promoter is recognized by RNA polymerase II, and is more amenable for expression of long RNA stretches than is RNAP III. The promoter precedes the interfering RNA, such as an shRNA, siRNA or miRNA, as described above.

In eukaryotic cells, DNA is transcribed by three types of RNA polymerases; RNA Pol I, II and III. RNA Pol I transcribes only ribosomal RNA (rRNA) genes, RNA Pol II transcribes DNA into mRNA and small nuclear RNAs (snRNAs), and RNA Pol III transcribes DNA into ribosomal 5S rRNA (type I), transfer RNA (tRNA) (type II) and other small RNAs such as U6 snRNAs (type III). shRNAs are typically transcribed in vivo under the control of eukaryotic type III RNA Pol III promoters, such as the human U6 promoter, which transcribes the U6 snRNA component of the spliceosome, and the H1 human promoter, which transcribes the RNA component of RNase P. U6 and H1 promoters are more suitable than other Pol III or Pol II promoters because they are structurally simple, with a well-defined transcription start-site, and naturally drive the transcription of small RNAs. U6 and H1 promoters do not carry the sequences necessary for transcribing anything downstream from the transcription start site (Makinen et al. (2006) J. Gene Med. 8:433-441). They are thus the most straightforward promoters for use in shRNA expression.

The use of other promoters such as type II pol III tRNA promoters, while successful in expressing shRNAs, results in longer dsRNA transcripts, which can induce an interferon response. RNA pol II promoters, such as the human cytomegalovirus (CMV) promoter also can be used (U.S. Pat. Nos. 8,202,846 and 8,383,599), but are more often utilized for expression of long RNA stretches. Studies have shown that the addition of the enhancer from the CMV promoter near the U6 promoter can increase its activity, increasing shRNA synthesis and improving gene silencing (Xia et al. (2003) Nucleic Acids Res. 31(17):e100; Nie et al. (2010) Genomics Proteomics Bioinformatics 8(3):170-179). RNA pol II promoters are typically avoided in shRNA transcription due to the generation of cytoplasmic DNA, which leads to a pro-inflammatory interferon response. In this case, a cytoplasmic DNA mediated interferon response in S. typhimurium-infected tumor cells has anti-tumor benefit, especially in the context of TREX1 inhibition as provided herein. Prokaryotic promoters, including T7, pBAD and pepT promoters can be utilized when transcription occurs in a bacterial cell (Guo et al. (2011) Gene therapy 18:95-105; U.S. Patent Publication Nos. 2012/0009153, 2016/0369282; International Application Publication Nos. WO 2015/032165, WO 2016/025582).

RNA pol III promoters generally are used for constitutive shRNA expression. For inducible expression, RNA pol II promoters are used. Examples include the pBAD promoter, which is inducible by L-arabinose; tetracycline-inducible promoters such as TRE-tight, IPT, TRE-CMV, Tet-ON and Tet-OFF; retroviral LTR; IPTG-inducible promoters such as Lad, Lac-O responsive promoters; LoxP-stop-LoxP system promoters (U.S. Pat. No. 8,426,675; International Application Publication No. WO 2016/025582); and pepT, which is a hypoxia-induced promoter (Yu et al. (2012) Scientific Reports 2:436). These promoters are well known. Exemplary of these promoters are human U6 (SEQ ID NO:73) and human H1 (SEQ ID NO:74).

SEQ ID NO. Name Sequence 73 human U6                                              aa ggtcgggcag gaagagggcc RNA pol 721 tatttcccat gattccttca tatttgcata tacgatacaa ggctgttaga gagataatta III 781 gaattaattt gactgtaaac acaaagatat tagtacaaaa tacgtgacgt agaaagtaat promoter 841 aatttcttgg gtagtttgca gttttaaaat tatgttttaa aatggactat catatgctta 901 ccgtaacttg aaagtatttc gatttcttgg ctttatatat cttgtggaaa ggacgaaact 961 ag 74 human H1                                                  atatttgca tgtcgctatg RNA pol 721 tgttctggga aatcaccata aacgtgaaat gtctttggat ttgggaatct tataagttct III 781 gtatgagacc actccctagg promoter

Tissue specific promoters include TRP2 promoter for melanoma cells and melanocytes; MMTV promoter or WAP promoter for breast and breast cancer cells, Villin promoter or FABP promoter for intestinal cells, RIP promoter for pancreatic beta cells, Keratin promoter for keratinocytes, Probasin promoter for prostatic epithelium, Nestin promoter or GFAP promoter for CNS cells/cancers, Tyrosine Hydroxylase S100 promoter or neurofilament promoter for neurons, Clara cell secretory protein promoter for lung cancer, and Alpha myosin promoter in cardiac cells (U.S. Pat. No. 8,426,675).

8. DNA Nuclear Targeting Sequences

DNA nuclear targeting sequences (DTS) such as the SV40 DTS mediate the translocation of DNA sequences through the nuclear pore complex. The mechanism of this transport is reported to be dependent on the binding of DNA binding proteins that contain nuclear localization sequences. The inclusion of a DTS on a plasmid to increase nuclear transport and expression has been demonstrated (Dean, D. A. et al. (1999) Exp. Cell Res. 253(2):713-722), and has been used to increase gene expression from plasmids delivered by S. typhimurium (Kong et al. (2012) Proc. Natl. Acad. Sci. U.S.A. 109(47):19414-19419).

Rho-independent or class I transcriptional terminators such as the T1 terminator of the rrnB gene of E. coli contain sequences of DNA that form secondary structures that cause dissociation of the transcription elongation complex. Transcriptional terminators shall be included in the plasmid in order to prevent expression of interfering RNAs by the S. typhimurium transcriptional machinery. This ensures that expression of the encoded interfering RNA, such as shRNA, micro-RNA and siRNA, is confined to the host cell transcriptional machinery.

Plasmids used for transformation of Salmonella, such as S. typhimurium, as a cancer therapy described herein, contain all or some of the following attributes: 1) a CpG island, 2) a bacterial origin of replication, 3) an asd gene selectable marker for plasmid maintenance, 4) one or more human interfering RNA expression cassettes, 5) DNA nuclear targeting sequence, and 6) transcriptional terminators.

9. CRISPR

An immunostimulatory bacterium, encoding a CRISPR cassette, can be used to infect human immune, myeloid, or hematopoietic cells in order to site-specifically knockout a target gene of interest. The strain used can be asd⁻ and can contain a plasmid that lacks the complementary asd cassette and contains a kan cassette. In order to grow the strain in vitro in liquid media, DAP is added to complement the asd⁻ genetic deficiency. After infection of human cells, the strain can no longer replicate, and the CRISPR cassette-encoded plasmid is delivered. The strain also can be hilA⁻ or can lack one or more parts of SPI-1, or lack flagellin, or any combination thereof, which reduces or prevents pyroptosis (inflammatory-mediated cell death) of phagocytic cells.

G. TUMOR-TARGETING IMMUNOSTIMULATORY BACTERIA CONTAIN RNAI AGAINST EXEMPLARY IMMUNE TARGET GENES TO STIMULATE ANTI-TUMOR IMMUNITY

RNAi against any immune target can be encoded in the plasmids. These include, but are not limited to, any discussed in the disclosure herein, and any known to those of skill in the art. The following discussion describes exemplary targets. The plasmids can contain any RNAi against such targets, including, but not limited to, shRNA, siRNA and microRNA.

1. TREX1

In certain embodiments provided herein, the immunostimulatory bacteria encode inhibitory RNA, such as shRNA, that inhibit or disrupt or suppress TREX1 expression. The enzyme product encoded by TREX1, located upstream from cGAS, is a mediator of the type I interferon pathway. TREX1 encodes the major 3′ DNA exonuclease in mammalian cells (also called DNase III). Human TREX1 proteins are as catalytically efficient as bacterial exonucleases (Mazur and Perrino (2001) J. Biol. Chem. 276:17022-17029). Immunostimulatory bacterium that inhibit TREX1 expression by processes other than RNA silencing also are contemplated herein.

For the immunostimulatory bacteria provided herein, such as those that express shRNA against TREX1, loss of TREX1 activity and subsequent activation of cGAS/STING-induced vascular disruption enhances tumor colonization of S. typhimurium. The TREX1 gene encodes a protein that is 314 amino acids long (Mazur et al. (2001) J. Biol. Chem 276:17022-17029), exists as a homodimer, and lacks endonuclease activity. TREX1 is among several proteins involved in the repair of DNA that is damaged by exogenous genotoxic stress, including UV irradiation and DNA-damaging compounds. TREX1 can function as an editing exonuclease for DNA pol β by excising mispaired nucleotides from the 3′ end (Mazur et al. (2001) J. Biol. Chem 276:17022-17029). ssDNA is degraded 3-4 times more efficiently than dsDNA (Lindahl et al. (2009) Biochem. Soc. Trans. 37 (Pt 3), 535-538). Mutations in residues D18 and D200, frequently associated with autoimmune diseases, disable TREX1 enzyme from degrading dsDNA and reduces its ability to degrade ssDNA. TREX1 enzyme translocates from the endoplasmic reticulum to the nucleus following DNA damage, indicating its involvement in the replication of damaged DNA. Promoter activation and upregulation of TREX1 has been observed as a result of UVC exposure in mouse fibroblasts, and TREX1 null mouse cells have demonstrated hypersensitivity to UVC light (Tomicic et al. (2013) Bioch. Biophys. Acta 1833:1832-1843).

Mutations resulting in loss of TREX1 have been identified in patients with the inherited rare disease, Aicardi-Goutieres syndrome (AGS), which has phenotypic overlap with the autoimmune diseases systemic lupus erythematosus (SLE) and chilblain lupus (Aicardi and Goutieres, (2000) Neuropediatrics 31(3): 113). Mutations in TREX1 also are associated with retinal vasculopathy with cerebral leukodystrophy. TREX1-mediated autoimmune diseases are associated with the cell's inability to prevent autoimmunity via the degradation of ssDNA and dsDNA that accumulates in the cytoplasm. TREX1 null mice suffer from inflammatory myocarditis, resulting in circulatory failure, which is caused by chronic cytokine production (Morita et al. (2004) Mol. Cell Biol. 24(15):6719-6727; Yang et al. (2007) Cell 131(5):873-886; Tomicic et al. (2013) Bioch. Biophys. Acta 1833(8):1832-1843). Hence, TREX1 deficiency induces innate immunity following the cytoplasmic accumulation of DNA, resulting in an inflammatory response (Wang et al. (2009) DNA Repair(Amst) 8:1179-1189). The source of the DNA that accumulates in the cytosol of TREX1-deficient cells was found to be in part derived from endogenous retroelements that escape from the damaged nucleus, as TREX1 is known to metabolize reverse-transcribed (RT) DNA (Stetson et al. (2008) Cell 134(4):587-598). In HIV infection, HIV RT DNA accumulates in the cytosol of infected T cells and macrophages, and would normally trigger cGAS/STING activation of antiviral immunity. TREX1 digests this viral DNA and permits HIV immune escape (Yan et al. (2010) Nat. Immunol. 11(11): 1005-1013). Thus, TREX1 acts as a negative regulator of STING, and can be exploited to evade detection by several retroviruses, such as murine leukemia virus (MLV), simian immunodeficiency virus (SIV), and many others (Hasan et al. (2014) Front. Microbiol. 5:193).

Like STING, TREX1 is expressed in most mammalian cell types, with the key producers of cytokines in TREX1 null mice originating from macrophages and dendritic cells (Ahn et al. (2014) J. Immunol. 193(9):4634-4642). Data indicate that TREX1 is responsible for degrading self-DNA that can leak from a damaged nucleus into the cytosol, where it would otherwise bind and activate cGAS and lead to autoimmunity (Barber (2015) Nat. Rev. Immunol. 15(12):760-770). In support of this, TREX1 null mice and TREX1-deficient cells that also lack cGAS are completely protected from type I interferon activation and lethal autoimmunity (Ablasser et al. (2014) J. Immunol. 192(12):5993-5997; Gray et al. (2015) J. Immunol. 195(5):1939-1943). In a negative feedback loop, type I interferon and type II IFNγ can also induce TREX1, and TREX1 thus serves to limit aberrant autoimmune activation (Tomicic et al. (2013) Bioch. Biophys. Acta 1833:1832-1843).

Lymphocytes derived from an Aicardi-Goutieres syndrome patient, containing mutated TREX1, were found to inhibit angiogenesis and the growth of neuroblastoma cells, the effect being enhanced by the presence of IFN-α (Pulliero et al. (2012) Oncology Reports 27:1689-1694). The use of microRNA-103 also has been shown to inhibit the expression of TREX1, disrupting DNA repair and angiogenesis, and resulting in decreased tumor growth in vivo (see, U.S. Patent Publication No. 2014/0127284, Cheresh et al.).

TREX1 is a negative regulator of macrophage activation and pro-inflammatory function. TREX1 null macrophages were found to exhibit increased TNF-α and IFN-α production, higher levels of CD86, and increased antigen presentation to T cells, as well as impaired apoptotic T cell clearance (Pereira-Lopes et al. (2013) J. Immunol. 191:6128-6135). The inability to adequately digest apoptotic DNA in TREX1 null macrophages generates high amounts of aberrant cytosolic DNA, which binds to cGAS and activates the STING pathway to produce higher levels of type I interferon (Ahn et al. (2014) J. Immunol. 193:4634-4642). Not all cell types are sensitive to the immunostimulatory effects of Trex1 knockdown, however. In a study of individual cell types, dendritic cells, macrophages, fibroblasts and keratinocytes were found to produce type I IFN upon TREX1 knockdown, while B cells, cardiomyocytes, neurons and astrocytes did not (Peschke et al. (2016) J. Immunol. 197:2157-2166). Thus, inhibiting the function of TREX1 in phagocytic cells that have engulfed S. typhimurium would enhance their pro-inflammatory activity, while driving an accumulation of cytosolic DNA from phagocytosed tumor cells that can then activate the cGAS/STING pathway. The use of microRNA-103 inhibits the expression of TREX1, disrupting DNA repair and angiogenesis, and resulting in decreased tumor growth in vivo (see, U.S. Publication No. 2014/0127284, Cheresh et al.).

Studies have found that the expression of cGAS and/or STING is inhibited in over a third of colorectal cancers, while STING expression is lost in many primary and metastatic melanomas and HPV⁺ cancers. STING signaling remains intact in all tumor-resident APCs that continuously sample the antigenic milieu of the TME, including Batf3-lineage CD103/CD8α⁺ DCs that cross-present tumor antigens to CD8⁺ T cells, and these APCs will also readily phagocytose S. typhimurium or be activated by type I IFN from neighboring macrophages that have phagocytosed S. typhimurium containing TREX1 gene knockdown.

Inactivation of TREX1 enhances an immune response by permitting cytosolic accumulation of dsDNA to bind to the enzyme cyclic GMP-AMP (cGAMP) synthase (cGAS), a cytosolic DNA sensor that triggers the production of type I interferons and other cytokines through activation of the STING signaling pathway (Sun et al. (2013) Science 339(6121):786-791; Wu et al. (2013) Science 339(6121):826-830). Activation of the STING pathway has been shown to induce potent innate and adaptive antitumor immunity (Corrales et al. (2015) Cell Reports 11:1018-1030).

Hence, embodiments of the immunostimulatory bacterial strains, as provided herein, are administered to inhibit TREX1 in tumor-resident APCs and induce cGAS/STING activation, thereby activating these DCs to cross-present host tumor antigens to CD8⁺ T cells and induce local and systemic tumor regression and durable anti-tumor immunity (Corrales et al. (2015) Cell Reports 11:1018-1030; Zitvogel et al. (2015) Nat. Rev. Mol. Cell. Biol. 16:393-405).

Immunostimulatory bacteria provided herein express RNAi against TREX1, and loss of TREX1 and subsequent activation of cGAS/STING-induced vascular disruption enhance tumor colonization of S. typhimurium.

2. PD-L1

Programmed cell death protein 1 (PD-1) is an immune-inhibitory receptor that is involved in the negative regulation of immune responses. Its cognate ligand, programmed death-ligand 1 (PD-L1), is expressed on APCs, and upon binding to PD-1 on T cells, leads to loss of CD8⁺ T cell effector function, inducing T cell tolerance. The expression of PD-L1 is often associated with tumor aggressiveness and reduced survival in certain human cancers (Gao et al. (2009) Clin. Cancer Res. 15(3):971-979).

Antibodies designed to block immune checkpoints, such as anti-PD-1 (for example, pembrolizumab, nivolumab) and anti-PD-L1 (for example, atezolizumab, avelumab, durvalumab) antibodies have had durable success in preventing T cell anergy and breaking immune tolerance. Only a fraction of treated patients exhibit clinical benefit, and those that do often present with autoimmune-related toxicities (Ribas (2015) N. Engl. J. Med. 373(16):1490-1492; Topalian et al. (2012) N. Engl. J. Med. 366(26):2443-54). Besides acquiring toxicity, PD-1/PD-L1 therapy often leads to resistance, and the concomitant use of anti-CTLA-4 antibodies (for example, ipilimumab) has shown limited success in clinical trials with significantly additive toxicity. To limit the toxicity and enhance the potency of PD-L1 blockade, an immunostimulatory bacteria with an shRNA to PD-L1, as provided herein, will synergize with TLR activation of immune cells to both activate and potentiate anti-tumor immunity.

3. VISTA

Other non-redundant checkpoints in immune activation can synergize with PD-1/PD-L1 and CTLA-4, such as V-domain immunoglobulin (Ig) suppressor of T cell activation (VISTA). VISTA is expressed primarily on APCs, particularly on tumor-infiltrating myeloid cells and myeloid-derived suppressor cells (MDSC), and to a lesser extent on regulatory T cells (CD4⁺ Foxp3⁺ Tregs) (Wang et al. (2011) J. Exp. Med. 208(3):577-592). Similar to PD-L1, VISTA upregulation directly suppresses T cell proliferation and cytotoxic function (Liu et al. (2015) Proc. Natl. Acad. Sci. U.S.A. 112(21):6682-6687). Monoclonal antibody targeting of VISTA was shown to remodel the tumor microenvironment in mice, increasing APC activation and enhancing anti-tumor immunity (LeMercier et al. (2014) Cancer Res. 74(7): 1933-1944). Clinically, VISTA expression was shown to be upregulated on tumor-resident macrophages following treatment with anti-CTLA-4 therapy in prostate cancer, demonstrating compensatory regulation of immune checkpoints (Gao et al. (2017) Nat. Med. 23(5):551-555). The majority of VISTA expression is purported to be located in the intracellular compartment of myeloid cells, rather than on the surface, which can limit the effectiveness of the monoclonal antibody approach (Deng et al. (2016) J. Immunother. Cancer 4:86). The ability to inhibit VISTA from within the APC using a tumor-targeting bacteria containing shRNA to VISTA, as provided herein, will more efficiently and completely inhibit the T cell-suppressing function of VISTA, leading to activation of T cell-mediated anti-tumor immunity and tumor regression.

4. SIRPα

One mechanism by which tumor cells evade removal is to prevent their phagocytosis by innate immune cells. Phagocytosis is inhibited by surface expression of CD47, which is widely expressed on hematopoietic and non-hematopoietic cells (Liu et al. (2015) PLoS ONE 10(9):e0137345). Upon CD47 binding its receptor, signal regulatory protein alpha (SIRPα), an inhibitory signal for phagocytosis, is initiated. SIRPα is abundantly expressed on phagocytic cells, including macrophages, granulocytes and DCs. As such, the protein-protein interaction between CD47 and SIRPα represents another class of immune checkpoints unique to APCs, and tumor-resident macrophages in particular. The effectiveness of CD47 in preventing phagocytosis is evidenced by the fact that it is often upregulated in a wide variety of tumors, which allow them to avoid being phagocytosed by APCs in the tumor microenvironment (Liu et al. (2015) Nat. Med. 21(10):1209-1215). Several methods to block the CD47/SIRPα interaction have been examined, including the development of anti-CD47 or anti-SIRPα antibodies or antibody fragments, the use of small peptides that bind either protein, or the knockdown of CD47 expression (U.S. Patent Publication Nos. 2013/0142786, 2014/0242095; International Application Publication No. WO 2015/191861; McCracken et al. (2015) Clin. Cancer Res. 21(16):3597-3601). To this end, several monoclonal antibodies that directly target SIRPα are in clinical development, either alone or in combination with tumor-targeting antibodies (e.g., Rituximab, Daratumumab, Alemtuzumab, Cetuximab) that can enhance phagocytosis of antibody-opsonized tumor cells, in a process known as antibody-dependent cellular phagocytosis (ADCP) (McCracken et al. (2015) Clin. Cancer Res. 21(16):3597-3601; Yanagita et al. (2017) JCI Insight 2(1):e89140).

The CD47/SIRPα interaction also serves to preserve the longevity of red blood cells by preventing their phagocytic elimination (Murata et al. (2014) J. Biochem. 155(6):335-344). Thus, systemically administered therapies such as anti-CD47 antibodies that broadly disrupt this interaction have resulted in anemia toxicities (Huang et al. (2017) J. Thorac. Dis. 9(2):E168-E174). Systemic SIRPα-based therapies also risk adverse events, such as organ damage by creating systemic hyperphagocytic self-eating macrophages. Using a tumor-targeting immunostimulatory bacteria containing an shRNA to SIRPα, such as provided herein, will localize the CD47/SIRPα disruption to the tumor microenvironment and eliminate these adverse events. Further, inhibition of SIRPα in the context of bacterial activation of TLR-mediated pro-inflammatory signaling pathways will potently activate these macrophages to become hyperphagocytic towards neighboring tumor cells (Bian et al. (2016) Proc. Natl. Acad. Sci. U.S.A. 113(37): E5434-E5443).

5. β-catenin

Immune checkpoint pathways exemplify the multiple layers of regulation that exist to prevent immune hyper-activation and autoimmunity, and the difficulties in subverting these pathways to promote anti-tumor immunity. One mechanism by which tumors have evolved to be refractory to checkpoint therapies is through their lack of T cell and dendritic cell (DC) infiltration, described as non-T-cell-inflamed, or “cold tumors” (Sharma et al. (2017) Cell 9; 168(4):707-723). Several tumor-intrinsic mechanisms have been identified that lead to the exclusion of anti-tumor T cells and resistance to immunotherapy. In melanoma, in particular, molecular profiling of checkpoint therapy-refractory tumors revealed a signature of elevated β-catenin and its downstream target genes, correlating with a lack of tumor-infiltrating lymphocytes (Gajewski et al. (2011) Curr. Opin. Immunol. 23(2):286-292).

CTNNB1 is an oncogene that encodes β-catenin, and can induce the expression of the genes c-Myc and cyclin D1, resulting in tumor proliferation. Mutations in CTNNB1 are associated with certain cancers. Gene silencing of CTNNB1/β-catenin using S. typhimurium shRNA vectors can be used in the treatment of cancer (Guo et al. (2011) Gene therapy 18:95-105; U.S. Patent Publication Nos. 2012/0009153, 2016/0369282; International Patent Publication No. WO 2015/032165). For example, shRNA silencing of CTNNB1, using S. typhimurium strain SL7207 as a delivery vector, reduced tumor proliferation and growth in SW480 xenograft mice, when compared to control cells, and reduced expression of c-Myc and cyclin D1(Guo et al. (2011) Gene therapy 18:95-105). Silencing of CTNNB1 for the treatment of hepatoblastoma also can be achieved using miRNA, with or without antibody therapeutics against the immune checkpoints PD-land PD-L1 (International Application Publication No. WO 2017/005773). The use of siRNA or shRNA targeting CTNNB1, delivered via alternative vectors, such as liposomes, for the treatment of CTNNB1-related cancers, including adenocarcinomas and squamous cell carcinomas, also can be affected (U.S. Patent Publication Nos. 2009/0111762, 2012/0294929).

Elevated β-catenin signaling directly inhibits the chemokine CCL4 from recruiting Batf3-lineage CD103/CD8α⁺ DCs, thereby preventing them from priming tumor antigen-specific CD8⁺ T cells (Spranger et al. (2015) Nature 523(7559):231-235). β-catenin is the major downstream mediator of the WNT signaling pathway, a key embryonic developmental pathway that is also critical for adult tissue regeneration, homeostasis and hematopoiesis (Clevers et al. (2012) Cell 149(6):1192-1205). Excessive WNT/β-catenin signaling has been implicated in a variety of cancers (Tai et al. (2015) Oncologist 20(10):1189-1198). Accordingly, several strategies to target WNT/β-catenin signaling have been pursued, but success has been hampered by a lack of specificity to the tumor microenvironment, resulting in off-target toxicities to intestinal stem cells, bone turnover and hematopoiesis (Kahn (2014) Nat. Rev. Drug Dis. 13(7):513-532). The immunostimulatory bacteria provided herein overcome these problems.

For example, an advantage of using an immunostimulatory bacteria with shRNA to β-catenin as provided herein, is enhancing chemokine-mediated infiltration of T cell-priming DCs and the conversion of a cold tumor to a T-cell-inflamed tumor microenvironment, without the systemic toxicities of existing therapeutic modalities. Further, bacterial activation of TLR innate immune signaling pathways synergize with β-catenin inhibition to further promote immune activation and anti-tumor immunity.

6. TGF-β

Transforming growth factor beta (TGF-β) is a pleiotropic cytokine with numerous roles in embryogenesis, wound healing, angiogenesis and immune regulation. It exists in three isoforms in mammalian cells, TGF-β1, TGF-β2 and, TGF-β3; TGF-β1 is the most predominant in immune cells (Esebanmen et al. (2017) Immunol Res. 65:987-994). TGF-β's role as an immunosuppressant is arguably its most dominant function. Its activation from a latent form in the tumor microenvironment, in particular, has profound immunosuppressive effects on DCs and their ability to tolerize antigen-specific T cells. TGF-β can also directly convert Th1 CD4⁺ T cells to immunosuppressive Tregs, furthering promoting tumor tolerance (Travis et al. (2014) Annu. Rev. Immunol. 32:51-82). Based on its tumor-specific immunosuppressive functions, and irrespective of its known cancer cell growth and metastasis-promoting properties, inhibition of TGF-β is a cancer therapy target. High TGF-β signaling has been demonstrated in several human tumor types, including CRC, HCC, PDAC and NSCLC (Colak et al. (2017) Trends in Cancer 3:1). Systemic inhibition of TGF-β can lead to unacceptable autoimmune toxicities, and its inhibition should be localized to the tumor microenvironment. As such, a tumor-targeting immunostimulatory bacteria with RNAi, such as shRNA, to TGF-β, provided herein, or an shRNA to TGF-βRII, breaks tumor immune tolerance and stimulates anti-tumor immunity.

7. VEGF

Angiogenesis, or the development of new blood vessels, is an essential step for any tumor microenvironment to become established. Vascular endothelial growth factor (VEGF) is the critical mitogen for endothelial proliferation and angiogenesis, and inhibition of VEGF in the tumor microenvironment markedly decreases tumor vascularity, thereby starving the tumor of its blood supply (Kim et al. (1993) Nature 362(6423):841-4). This early research led to the development of the monoclonal antibody inhibitor of VEGF, bevacizumab (Avastin; Genentech), which in combination with chemotherapy, has become the standard of care for metastatic CRC. Systemic administration of bevacizumab also demonstrated significant toxicities, including multiple fatalities in a Phase II trial of NSCLC, largely due to hemorrhaging. As such, several next generation anti-angiogenics have been evaluated, such as the anti-VEGF receptor 2 antibody ramucirumab (Cyramza, Imclone) and the anti-angiogenic tyrosine kinase inhibitor axitinib (Inlyta, Pfizer), yet none have been able to overcome systemic toxicity or markedly improve progression-free survival (Alshangiti et al. (2018) Curr. Oncol. 25(Suppl 1):S45-S58). While the anti-tumor activity of anti-VEGF therapy has shown some promise, systemic toxicity is clearly limiting. As such, a therapy that targets only the tumor microenvironment, such as an immunostimulatory tumor-targeting bacteria with shRNA to VEGF, provided herein, delivers local anti-angiogenic therapy while preventing systemic toxicity. This therapeutic modality has the additional advantage of being taken up into myeloid cells, which predominantly produce VEGF in the tumor microenvironment, where it will have maximum impact on tumor progression (Osterberg et al. (2016) Neuro-Oncology. 18(7):939-949).

8. Additional Exemplary Checkpoint Targets

Exemplary checkpoint targets for which RNAi, such as micro-RNA and shRNA, can be prepared or are exemplified herein include, but are not limited to:

Checkpoint target CTLA-4 PD-L1 (B7-H1) PD-L2 PD-1, PD-2 IDO1 IDO2 SIRP alpha, CD47 VISTA (B7-H5) LIGHT HVEM CD28 LAG3, TIM3, TIGIT Galectin-9 CEACAM1, CD155, CD112, CD226, CD244 (2B4), B7-H2, B7-H3, CD137, ICOS, GITR, B7-H4, B7-H6 CD137, CD27, CD40/CD40L, CD48, CD70, CD80, CD86, CD137 (4-1BB), CD200, CD272 (BTLA), CD160 A2a receptor, A2b receptor, HHLA2, ILT-2, ILT-4, gp49B, PIR-B OX40/OX-40L, BTLA, ICOS, HLA-G, ILT-2/4 KIR, GITR, TIM1, TIM4 Other exemplary targets include, but are not limited to:

Target CTNNB1 (beta-catenin) STAT3 BCL-2 MDR1 Arginase1 iNOS TGF-β IL-10 pGE2 VEGF KSP HER2 KRAS TAK1 PLK1 K-Ras (Ras) Stablin-1/CLEVER-1 RNase H2 DNase II

H. PHARMACEUTICAL PRODUCTION, COMPOSITIONS, AND FORMULATIONS

Provided herein are methods for manufacturing, pharmaceutical compositions and formulations containing any of the immunostimulatory bacteria provided herein and pharmaceutically acceptable excipients or additives. The pharmaceutical compositions can be used in treatment of diseases, such as hyperproliferative diseases or condition, such as a tumor or cancer. The immunostimulatory bacteria can be administered in a single agent therapy, or can be administered in a combination therapy with a further agent or treatment. The compositions can be formulated for single dosage administration or for multiple dosage administration. The agents can be formulated for direct administration. The compositions can be provided as a liquid or dried formulation.

1. Manufacturing

a. Cell Bank Manufacturing

As the active ingredient of the immunotherapeutic described herein is composed of engineered self-replicating bacteria, the selected composition will be expanded into a series of cell banks that will be maintained for long-term storage and as the starting material for manufacturing of drug substance. Cell banks are produced under current good manufacturing practices (cGMP) in an appropriate manufacturing facility per the Code of Federal Regulations (CFR) 21 part 211 or other relevant regulatory authority. As the active agent of the immunotherapeutic is a live bacterium, the products described herein are, by definition, non-sterile and cannot be terminally sterilized. Care must be taken to ensure that aseptic procedures are used throughout the manufacturing process to prevent contamination. As such, all raw materials and solutions must be sterilized prior to use in the manufacturing process.

A master cell bank (MCB) is produced by sequential serial single colony isolation of the selected bacterial strain to ensure no contaminants are present in the starting material. A sterile culture vessel containing sterile media (can be complex media e.g., LB or MSBB or defined media e.g., M9 supplemented with appropriate nutrients) is inoculated with a single well-isolated bacterial colony and the bacteria are allowed to replicate e.g., by incubation at 37° C. with shaking. The bacteria are then prepared for cryopreservation by suspension in a solution containing a cryoprotective agent or agents.

Examples of cryoprotective agents include: proteins such as human or bovine serum albumin, gelatin, and immunoglobulins; carbohydrates including monosaccharides (galactose, D-mannose, sorbose, etc.) and their non-reducing derivatives (e.g., methylglucoside), disaccharides (trehalose, sucrose, etc.), cyclodextrins, and polysaccharides (raffinose, maltodextrins, dextrans, etc.); amino-acids (glutamate, glycine, alanine, arginine or histidine, tryptophan, tyrosine, leucine, phenylalanine, etc.); methylamines such as betaine; polyols such as trihydric or higher sugar alcohols, e.g., glycerin, erythritol, glycerol, arabitol, xylitol, sorbitol, and mannitol; propylene glycol; polyethylene glycol; surfactants e.g., pluronic; or organo-sulfur compounds such as dimethyl sulfoxide (DMSO), and combinations thereof. Cryopreservation solutions can include one or more cryoprotective agents in a solution that can also contain salts (e.g., sodium chloride, potassium chloride, magnesium sulfate), and/or buffering agents such as sodium phosphate, tris(hydroxymethyl)aminomethane (TRIS), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), and other such buffering agents known to those of skill.

Suspension of the bacteria in cryopropreservation solution can be achieved either by addition of a concentrated cryoprotective agent or agents to the culture material to achieve a final concentration that preserves viability of the bacteria during the freezing and thawing process (e.g., 0.5% to 20% final concentration of glycerol), or by harvesting the bacteria (e.g., by centrifugation) and suspending in a cryopreservative solution containing the appropriate final concentration of cryoprotective agent(s). The suspension of bacteria in cryopreservation solution is then filled into appropriate sterile vials (plastic or glass) with a container closure system that is capable of maintaining closure integrity under frozen conditions (e.g., butyl stoppers and crimp seals). The vials of master cell bank are then frozen (either slowly by means of a controlled rate freezer, or quickly by means of placing directly into a freezer). The MCB is then stored frozen at a temperature that preserves long-term viability (e.g., at or below −60° C.). Thawed master cell bank material is thoroughly characterized to ensure identity, purity, and activity per regulation by the appropriate authorities.

Working cell banks (WCBs) are produced much the same way as the master cell bank, but the starting material is derived from the MCB. MCB material can be directly transferred into a fermentation vessel containing sterile media and expanded as above. The bacteria are then suspended in a cryopreservation solution, filled into containers, sealed, and frozen at or below −20° C. Multiple WCBs can be produced from MCB material, and WCB material can be used to make additional cell banks (e.g., a manufacturer's working cell bank MWCB). WCBs are stored frozen and characterized to ensure identity, purity, and activity. WCB material is typically the starting material used in production of the drug substance of biologics such as engineered bacteria.

b. Drug Substance Manufacturing

Drug substance is manufactured using aseptic processes under cGMP as described above. Working cell bank material is typically used as starting material for manufacturing of drug substance under cGMP, however other cell banks can be used (e.g., MCB or MWCB). Aseptic processing is used for production of all cell therapies including bacterial cell-based therapies. The bacteria from the cell bank are expanded by fermentation, this can be achieved by production of a pre-culture (e.g., in a shake flask) or by direct inoculation of a fermenter. Fermentation is accomplished in a sterile bioreactor or flask that can be single-use disposable or re-usable. Bacteria are harvested by concentration (e.g., by centrifugation, continuous centrifugation, or tangential flow filtration). Concentrated bacteria are purified from media components and bacterial metabolites by exchange of the media with buffer (e.g., by diafiltration). The bulk drug product is formulated and preserved as an intermediate (e.g., by freezing or drying) or is processed directly into a drug product. Drug substance is tested for identity, strength, purity, potency, and quality.

c. Drug Product Manufacturing

Drug product is defined as the final formulation of the active substance contained in its final container. Drug product is manufactured using aseptic processes under cGMP. Drug product is produced from drug substance. Drug substance is thawed or reconstituted if necessary, then formulated at the appropriate target strength. Because the active component of the drug product is live, engineered bacteria, the strength is determined by the number of CFUs contained within the suspension. The bulk product is diluted in a final formulation appropriate for storage and use as described below. Containers are filled, and sealed with a container closure system and the drug product is labeled. The drug product is stored at an appropriate temperature to preserve stability and is tested for identity, strength, purity, potency, and quality and released for human use if it meets specified acceptance criteria.

2. Compositions

Pharmaceutically acceptable compositions are prepared in view of approvals for a regulatory agency or other agency prepared in accordance with generally recognized pharmacopeia for use in animals and in humans. The compositions can be prepared as solutions, suspensions, powders, or sustained release formulations. Typically, the compounds are formulated into pharmaceutical compositions using techniques and procedures well known in the art (see e.g., Ansel Introduction to Pharmaceutical Dosage Forms, Fourth Edition, 1985, 126). The formulation should suit the mode of administration.

Compositions can be formulated for administration by any route known to those of skill in the art including intramuscular, intravenous, intradermal, intralesional, intraperitoneal injection, subcutaneous, intratumoral, epidural, nasal, oral, vaginal, rectal, topical, local, otic, inhalational, buccal (e.g., sublingual), and transdermal administration or any route. Other modes of administration also are contemplated. Administration can be local, topical or systemic depending upon the locus of treatment. Local administration to an area in need of treatment can be achieved by, for example, but not limited to, local infusion during surgery, topical application, e.g., in conjunction with a wound dressing after surgery, by injection, by means of a catheter, by means of a suppository, or by means of an implant. Compositions also can be administered with other biologically active agents, either sequentially, intermittently or in the same composition. Administration also can include controlled release systems including controlled release formulations and device controlled release, such as by means of a pump.

The most suitable route in any given case depends on a variety of factors, such as the nature of the disease, the progress of the disease, the severity of the disease and the particular composition which is used. Pharmaceutical compositions can be formulated in dosage forms appropriate for each route of administration. In particular, the compositions can be formulated into any suitable pharmaceutical preparations for systemic, local intraperitoneal, oral or direct administration. For example, the compositions can be formulated for administration subcutaneously, intramuscularly, intratumorally, intravenously or intradermally. Administration methods can be employed to decrease the exposure of the active agent to degradative processes, such as immunological intervention via antigenic and immunogenic responses. Examples of such methods include local administration at the site of treatment or continuous infusion.

The immunostimulatory bacteria can be formulated into suitable pharmaceutical preparations such as solutions, suspensions, tablets, dispersible tablets, pills, capsules, powders, sustained release formulations or elixirs, for oral administrations, as well as transdermal patch preparation and dry powder inhalers. Typically, the compounds are formulated into pharmaceutical compositions using techniques and procedures well known in the art (see e.g., Ansel Introduction to Pharmaceutical Dosage Forms, Fourth Edition, 1985, 126). Generally, the mode of formulation is a function of the route of administration. The compositions can be formulated in dried (lyophilized or other forms of vitrification) or liquid form. Where the compositions are provided in dried form they can be reconstituted just prior to use by addition of an appropriate buffer, for example, a sterile saline solution.

3. Formulations

a. Liquids, Injectables, Emulsions

The formulation generally is made to suit the route of administration. Parenteral administration, generally characterized by injection or infusion, either subcutaneously, intramuscularly, intratumorally, intravenously or intradermally is contemplated herein. Preparations of bacteria for parenteral administration include suspensions ready for injection (direct administration) or frozen suspensions that are thawed prior to use, dry soluble products, such as lyophilized powders, ready to be combined with a resuspension solution just prior to use, and emulsions. Dried thermostable formulations such as lyophilized formulations can be used for storage of unit doses for later use.

The pharmaceutical preparation can be in a frozen liquid form, for example a suspension. If provided in frozen liquid form, the drug product can be provided as a concentrated preparation to be thawed and diluted to a therapeutically effective concentration before use.

The pharmaceutical preparations also can be provided in a dosage form that does not require thawing or dilution for use. Such liquid preparations can be prepared by conventional means with pharmaceutically acceptable additives, as appropriate, such as suspending agents (e.g., sorbitol, cellulose derivatives or hydrogenated edible fats); emulsifying agents (e.g., lecithin or acacia); non-aqueous vehicles (e.g., almond oil, oily esters, or fractionated vegetable oils); and preservatives suitable for use with microbial therapeutics. The pharmaceutical preparations can be presented in dried form, such as lyophilized or spray-dried, for reconstitution with water or other sterile suitable vehicle before use.

Suitable excipients are, for example, water, saline, dextrose, or glycerol. The solutions can be either aqueous or non-aqueous. If administered intravenously, suitable carriers include physiological saline or phosphate buffered saline (PBS), and other buffered solutions used for intravenous hydration. For intratumoral administration solutions containing thickening agents such as glucose, polyethylene glycol, and polypropylene glycol, oil emulsions and mixtures thereof can be appropriate to maintain localization of the injectant.

Pharmaceutical compositions can include carriers or other excipients. For example, pharmaceutical compositions provided herein can contain any one or more of a diluents(s), adjuvant(s), antiadherent(s), binder(s), coating(s), filler(s), flavor(s), color(s), lubricant(s), glidant(s), preservative(s), detergent(s), or sorbent(s) and a combination thereof or vehicle with which a modified therapeutic bacteria is administered. For example, pharmaceutically acceptable carriers or excipients used in parenteral preparations include aqueous vehicles, non-aqueous vehicles, isotonic agents, buffers, antioxidants, local anesthetics, suspending and dispersing agents, emulsifying agents, sequestering or chelating agents and other pharmaceutically acceptable substances. Formulations, including liquid preparations, can be prepared by conventional means with pharmaceutically acceptable additives or excipients.

Pharmaceutical compositions can include carriers such as a diluent, adjuvant, excipient, or vehicle with which the compositions are administered. Examples of suitable pharmaceutical carriers are described in “Remington's Pharmaceutical Sciences” by E. W. Martin. Such compositions will contain a therapeutically effective amount of the compound or agent, generally in purified form or partially purified form, together with a suitable amount of carrier so as to provide the form for proper administration to the patient. Such pharmaceutical carriers can be sterile liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, such as peanut oil, soybean oil, mineral oil, and sesame oil. Water is a typical carrier. Saline solutions and aqueous dextrose and glycerol solutions also can be employed as liquid carriers, particularly for injectable solutions. Compositions can contain along with an active ingredient: a diluent such as lactose, sucrose, dicalcium phosphate, or carboxymethylcellulose; a lubricant, such as magnesium stearate, calcium stearate and talc; and a binder such as starch, natural gums, such as gum acacia, gelatin, glucose, molasses, polyvinylpyrrolidine, celluloses and derivatives thereof, povidone, crospovidones and other such binders known to those of skill in the art. Suitable pharmaceutical excipients include starch, glucose, lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, dried skim milk, glycerol, propylene, glycol, water, and ethanol. For example, suitable excipients are, for example, water, saline, dextrose, glycerol or ethanol. A composition, if desired, also can contain other minor amounts of non-toxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents, stabilizers, solubility enhancers, and other such agents, such as for example, sodium acetate, sorbitan monolaurate, triethanolamine oleate and cyclodextrins.

Pharmaceutically acceptable carriers used in parenteral preparations include aqueous vehicles, non-aqueous vehicles, antimicrobial agents, isotonic agents, buffers, antioxidants, local anesthetics, suspending and dispersing agents, emulsifying agents, sequestering or chelating agents and other pharmaceutically acceptable substances. Examples of aqueous vehicles include Sodium Chloride Injection, Ringers Injection, Isotonic Dextrose Injection, Sterile Water Injection, Dextrose and Lactated Ringers Injection. Non-aqueous parenteral vehicles include fixed oils of vegetable origin, cottonseed oil, corn oil, sesame oil and peanut oil. Isotonic agents include sodium chloride and dextrose. Buffers include phosphate and citrate. Antioxidants include sodium bisulfate. Local anesthetics include procaine hydrochloride. Suspending and dispersing agents include sodium carboxymethylcellulose, hydroxypropyl methylcellulose and polyvinylpyrrolidone. Emulsifying agents include, for example, polysorbates, such Polysorbate 80 (TWEEN 80). Sequestering or chelating agents of metal ions, such as EDTA, can be included. Pharmaceutical carriers also include polyethylene glycol and propylene glycol for water miscible vehicles and sodium hydroxide, hydrochloric acid, citric acid or lactic acid for pH adjustment. Non-anti-microbial preservatives can be included.

The pharmaceutical compositions also can contain other minor amounts of non-toxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents, stabilizers, solubility enhancers, and other such agents, such as for example, sodium acetate, sorbitan monolaurate, triethanolamine oleate and cyclodextrins. Implantation of a slow-release or sustained-release system, such that a constant level of dosage is maintained (see, e.g., U.S. Pat. No. 3,710,795) also is contemplated herein. The percentage of active compound contained in such parenteral compositions is highly dependent on the specific nature thereof, as well as the activity of the compound and the needs of the subject.

b. Dried Thermostable Formulations

The bacteria can be dried. Dried thermostable formulations, such as lyophilized or spray dried powders and vitrified glass can be reconstituted for administration as solutions, emulsions and other mixtures. The dried thermostable formulation can be prepared from any of the liquid formulations, such as the suspensions, described above. The pharmaceutical preparations can be presented in lyophilized or vitrified form for reconstitution with water or other suitable vehicle before use.

The thermostable formulation is prepared for administration by reconstituting the dried compound with a sterile solution. The solution can contain an excipient which improves the stability or other pharmacological attribute of the active substance or reconstituted solution, prepared from the powder. The thermostable formulation is prepared by dissolving an excipient, such as dextrose, sorbitol, fructose, corn syrup, xylitol, glycerin, glucose, sucrose or other suitable agent, in a suitable buffer, such as citrate, sodium or potassium phosphate or other such buffer known to those of skill in the art. Then, the drug substance is added to the resulting mixture, and stirred until it is mixed. The resulting mixture is apportioned into vials for drying. Each vial will contain a single dosage containing 1×10⁵ to 1×10¹¹ CFUs per vial. After drying, the product vial is sealed with a container closure system that prevents moisture or contaminants from entering the sealed vial. The dried product can be stored under appropriate conditions, such as at −20° C., 4° C., or room temperature. Reconstitution of this dried formulation with water or a buffer solution provides a formulation for use in parenteral administration. The precise amount depends upon the indication treated and selected compound. Such amount can be empirically determined.

4. Compositions for Other Routes of Administration

Depending upon the condition treated, other routes of administration in addition to parenteral, such as topical application, transdermal patches, oral and rectal administration are also contemplated herein. The suspensions and powders described above can be administered orally or can be reconstituted for oral administration. Pharmaceutical dosage forms for rectal administration are rectal suppositories, capsules and tablets and gel capsules for systemic effect. Rectal suppositories include solid bodies for insertion into the rectum which melt or soften at body temperature releasing one or more pharmacologically or therapeutically active ingredients. Pharmaceutically acceptable substances in rectal suppositories are bases or vehicles and agents to raise the melting point. Examples of bases include cocoa butter (theobroma oil), glycerin-gelatin, carbowax (polyoxyethylene glycol) and appropriate mixtures of mono-, di- and triglycerides of fatty acids. Combinations of the various bases can be used. Agents to raise the melting point of suppositories include spermaceti and wax. Rectal suppositories can be prepared either by the compressed method or by molding. The typical weight of a rectal suppository is about 2 to 3 gm. Tablets and capsules for rectal administration are manufactured using the same pharmaceutically acceptable substance and by the same methods as for formulations for oral administration. Formulations suitable for rectal administration can be provided as unit dose suppositories. These can be prepared by admixing the drug substance with one or more conventional solid carriers, for example, cocoa butter, and then shaping the resulting mixture.

For oral administration, pharmaceutical compositions can take the form of, for example, tablets or capsules prepared by conventional means with pharmaceutically acceptable excipients such as binding agents (e.g., pregelatinized maize starch, polyvinyl pyrrolidone or hydroxypropyl methylcellulose); fillers (e.g., lactose, microcrystalline cellulose or calcium hydrogen phosphate); lubricants (e.g., magnesium stearate, talc or silica); disintegrants (e.g., potato starch or sodium starch glycolate); or wetting agents (e.g., sodium lauryl sulfate). The tablets can be coated by methods well-known in the art.

Formulations suitable for buccal (sublingual) administration include, for example, lozenges containing the active compound in a flavored base, usually sucrose and acacia or tragacanth; and pastilles containing the compound in an inert base such as gelatin and glycerin or sucrose and acacia.

Topical mixtures are prepared as described for the local and systemic administration. The resulting mixtures can be solutions, suspensions, emulsions or the like and are formulated as creams, gels, ointments, emulsions, solutions, elixirs, lotions, suspensions, tinctures, pastes, foams, aerosols, irrigations, sprays, suppositories, bandages, dermal patches or any other formulations suitable for topical administration.

The compositions can be formulated as aerosols for topical application, such as by inhalation (see, e.g., U.S. Pat. Nos. 4,044,126; 4,414,209 and 4,364,923, which describe aerosols for delivery of a steroid useful for treatment of lung diseases). These formulations, for administration to the respiratory tract, can be in the form of an aerosol or solution for a nebulizer, or as a microfine powder for insufflation, alone or in combination with an inert carrier such as lactose. In such a case, the particles of the formulation will typically have diameters of less than 50 microns, or less than 10 microns.

The compounds can be formulated for local or topical application, such as for topical application to the skin and mucous membranes, such as in the eye, in the form of gels, creams, and lotions and for application to the eye or for intracisternal or intraspinal application. Topical administration is contemplated for transdermal delivery and also for administration to the eyes or mucosa, or for inhalation therapies. Nasal solutions of the active compound alone or in combination with other pharmaceutically acceptable excipients also can be administered.

Formulations suitable for transdermal administration are provided. They can be provided in any suitable format, such as discrete patches adapted to remain in intimate contact with the epidermis of the recipient for a prolonged period of time. Such patches contain the active compound in an optionally buffered aqueous solution of, for example, 0.1 to 0.2 M concentration with respect to the active compound. Formulations suitable for transdermal administration also can be delivered by iontophoresis (see, e.g., Tyle, P, (1986) Pharmaceutical Research 3(6):318-326) and typically take the form of an optionally buffered aqueous solution of the active compound.

Pharmaceutical compositions also can be administered by controlled release formulations and/or delivery devices (see e.g., U.S. Pat. Nos. 3,536,809; 3,598,123; 3,630,200; 3,845,770; 3,916,899; 4,008,719; 4,769,027; 5,059,595; 5,073,543; 5,120,548; 5,591,767; 5,639,476; 5,674,533 and 5,733,566).

5. Dosages and Administration

The compositions can be formulated as pharmaceutical compositions for single dosage or multiple dosage administration. The immunostimulatory bacteria can be included in an amount sufficient to exert a therapeutically useful effect in the absence of undesirable side effects on the patient treated. For example, the concentration of the pharmaceutically active compound is adjusted so that an injection provides an effective amount to produce the desired pharmacological effect. The therapeutically effective concentration can be determined empirically by testing the immunostimulatory bacteria in known in vitro and in vivo systems such as by using the assays described herein or known in the art. For example, standard clinical techniques can be employed. In vitro assays and animal models can be employed to help identify optimal dosage ranges. The precise dose, which can be determined empirically, can depend on the age, weight, body surface area, and condition of the patient or animal, the particular immunostimulatory bacteria administered, the route of administration, the type of disease to be treated and the seriousness of the disease.

Hence, it is understood that the precise dosage and duration of treatment is a function of the disease being treated and can be determined empirically using known testing protocols or by extrapolation from in vivo or in vitro test data. Concentrations and dosage values also can vary with the severity of the condition to be alleviated. It is to be further understood that for any particular subject, specific dosage regimens should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions, and that the concentration ranges set forth herein are exemplary only and are not intended to limit the scope or use of compositions and combinations containing them. The compositions can be administered hourly, daily, weekly, monthly, yearly or once. Generally, dosage regimens are chosen to limit toxicity. It should be noted that the attending physician would know how to and when to terminate, interrupt or adjust therapy to lower dosage due to toxicity, or bone marrow, liver or kidney or other tissue dysfunctions. Conversely, the attending physician would also know how to and when to adjust treatment to higher levels if the clinical response is not adequate (precluding toxic side effects).

The immunostimulatory bacteria are included in the composition in an amount sufficient to exert a therapeutically useful effect. For example, the amount is one that achieves a therapeutic effect in the treatment of a hyperproliferative disease or condition, such as cancer.

Pharmaceutically and therapeutically active compounds and derivatives thereof are typically formulated and administered in unit dosage forms or multiple dosage forms. Each unit dose contains a predetermined quantity of therapeutically active compound sufficient to produce the desired therapeutic effect, in association with the required pharmaceutical carrier, vehicle or diluent. Unit dosage forms, include, but are not limited to, tablets, capsules, pills, powders, granules, parenteral suspensions, and oral solutions or suspensions, and oil water emulsions containing suitable quantities of the compounds or pharmaceutically acceptable derivatives thereof. Unit dose forms can be contained in vials, ampoules and syringes or individually packaged tablets or capsules. Unit dose forms can be administered in fractions or multiples thereof. A multiple dose form is a plurality of identical unit dosage forms packaged in a single container to be administered in segregated unit dose form. Examples of multiple dose forms include vials, bottles of tablets or capsules or bottles of pints or gallons. Hence, multiple dose form is a multiple of unit doses that are not segregated in packaging. Generally, dosage forms or compositions containing active ingredient in the range of 0.005% to 100% with the balance made up from non-toxic carrier can be prepared. Pharmaceutical compositions can be formulated in dosage forms appropriate for each route of administration.

The unit-dose parenteral preparations are packaged in an ampoule, a vial or a syringe with a needle. The volume of liquid solution or reconstituted powder preparation, containing the pharmaceutically active compound, is a function of the disease to be treated and the particular article of manufacture chosen for package. All preparations for parenteral administration must be sterile, as is known and practiced in the art.

As indicated, compositions provided herein can be formulated for any route known to those of skill in the art including, but not limited to, subcutaneous, intramuscular, intravenous, intradermal, intralesional, intraperitoneal injection, epidural, vaginal, rectal, local, otic, transdermal administration or any route of administration. Formulations suited for such routes are known to one of skill in the art. Compositions also can be administered with other biologically active agents, either sequentially, intermittently or in the same composition.

Pharmaceutical compositions can be administered by controlled release formulations and/or delivery devices (see, e.g., U.S. Pat. Nos. 3,536,809; 3,598,123; 3,630,200; 3,845,770; 3,847,770; 3,916,899; 4,008,719; 4,687,660; 4,769,027; 5,059,595; 5,073,543; 5,120,548; 5,354,556; 5,591,767; 5,639,476; 5,674,533 and 5,733,566). Various delivery systems are known and can be used to administer selected compositions, are contemplated for use herein, and such particles can be easily made.

6. Packaging and Articles of Manufacture

Also provided are articles of manufacture containing packaging materials, any pharmaceutical composition provided herein, and a label that indicates that the compositions are to be used for treatment of diseases or conditions as described herein. For example, the label can indicate that the treatment is for a tumor or cancer.

Combinations of immunostimulatory bacteria described herein and another therapeutic agent also can be packaged in an article of manufacture. In one example, the article of manufacture contains a pharmaceutical composition containing the immunostimulatory bacteria composition and no further agent or treatment. In other examples, the article of manufacture contains another further therapeutic agent, such as a different anti-cancer agent. In this example, the agents can be provided together or separately, for packaging as articles of manufacture.

The articles of manufacture provided herein contain packaging materials. Packaging materials for use in packaging pharmaceutical products are well known to those of skill in the art. See, for example, U.S. Pat. Nos. 5,323,907, 5,052,558 and 5,033,252, each of which is incorporated herein in its entirety. Examples of pharmaceutical packaging materials include, but are not limited to, blister packs, bottles, tubes, inhalers, pumps, bags, vials, containers, syringes, bottles, and any packaging material suitable for a selected formulation and intended mode of administration and treatment. Exemplary of articles of manufacture are containers including single chamber and dual chamber containers. The containers include, but are not limited to, tubes, bottles and syringes. The containers can further include a needle for intravenous administration.

The choice of package depends on the agents, and whether such compositions will be packaged together or separately. In general, the packaging is non-reactive with the compositions contained therein. In other examples, some of the components can be packaged as a mixture. In other examples, all components are packaged separately. Thus, for example, the components can be packaged as separate compositions that, upon mixing just prior to administration, can be directly administered together. Alternatively, the components can be packaged as separate compositions for administration separately.

Selected compositions including articles of manufacture thereof also can be provided as kits. Kits can include a pharmaceutical composition described herein and an item for administration provided as an article of manufacture. The compositions can be contained in the item for administration or can be provided separately to be added later. The kit can, optionally, include instructions for application including dosages, dosing regimens and instructions for modes of administration. Kits also can include a pharmaceutical composition described herein and an item for diagnosis.

I. METHODS OF TREATMENT AND USES

The methods provided herein include methods of administering or using the immunostimulatory bacteria, for treating subjects having a disease or condition whose symptoms can be ameliorated or lessened by administration of such bacteria, such as cancer. In particular examples, the disease or condition is a tumor or a cancer. Additionally, methods of combination therapies with one or more additional agents for treatment, such as an anti-cancer agent, such as an oncolytic virus, an immunotherapeutic agent, and/or an anti-hyaluronan agent, such as a hyaluronidase, also are provided. The bacteria can be administered by any suitable route, including, but not limited to, parenteral, systemic, topical and local, such as intra-tumoral, intravenous, rectal, oral, intramuscular, mucosal and other routes. Because of the modifications of the bacteria described herein, problems associated with systemic administration, are solved. Formulations suitable for each route of administration are provided. The skilled person can establish suitable regimens and doses and select routes.

1. Tumors

The immunostimulatory bacteria, combinations, uses and methods provided herein are applicable to treating all types of tumors, including cancers, particularly solid tumors including lung cancer, bladder cancer, non-small cell lung cancer, gastric cancers, head and neck cancers, ovarian cancer, liver cancer, pancreatic cancer, kidney cancer, breast cancer, colorectal cancer, and prostate cancer. The methods also can be used for hematological cancers.

Tumors and cancers subject to treatment by the uses and methods provided herein include, but are not limited to, those that originate in the immune system, skeletal system, muscles and heart, breast, pancreas, gastrointestinal tract, central and peripheral nervous system, renal system, reproductive system, respiratory system, skin, connective tissue systems, including joints, fatty tissues, and circulatory system, including blood vessel walls. Examples of tumors that can be treated with the immunostimulatory bacteria provided herein include carcinomas, gliomas, sarcomas (including liposarcoma), adenocarcinomas, adenosarcomas, and adenomas. Such tumors can occur in virtually all parts of the body, including, for example, the breast, heart, lung, small intestine, colon, spleen, kidney, bladder, head and neck, ovary, prostate, brain, pancreas, skin, bone, bone marrow, blood, thymus, uterus, testicles, cervix or liver.

Tumors of the skeletal system include, for example, sarcomas and blastomas such as osteosarcoma, chondrosarcoma, and chondroblastoma. Muscle and heart tumors include tumors of both skeletal and smooth muscles, e.g., leiomyomas (benign tumors of smooth muscle), leiomyosarcomas, rhabdomyomas (benign tumors of skeletal muscle), rhabdomyosarcomas, and cardiac sarcomas. Tumors of the gastrointestinal tract include, e.g., tumors of the mouth, esophagus, stomach, small intestine, colon and colorectal tumors, as well as tumors of gastrointestinal secretory organs such as the salivary glands, liver, pancreas, and the biliary tract. Tumors of the central nervous system include tumors of the brain, retina, and spinal cord, and can also originate in associated connective tissue, bone, blood vessels or nervous tissue. Treatment of tumors of the peripheral nervous system are also contemplated. Tumors of the peripheral nervous system include malignant peripheral nerve sheath tumors. Tumors of the renal system include those of the kidneys, e.g., renal cell carcinoma, as well as tumors of the ureters and bladder. Tumors of the reproductive system include tumors of the cervix, uterus, ovary, prostate, testes and related secretory glands. Tumors of the immune system include both blood-based and solid tumors, including lymphomas, e.g., both Hodgkin's and non-Hodgkin's. Tumors of the respiratory system include tumors of the nasal passages, bronchi and lungs. Tumors of the breast include, e.g., both lobular and ductal carcinoma.

Other examples of tumors that can be treated by the immunostimulatory bacteria and methods provided herein include Kaposi's sarcoma, CNS neoplasms, neuroblastomas, capillary hemangioblastomas, meningiomas and cerebral metastases, melanoma, gastrointestinal and renal carcinomas and sarcomas, rhabdomyosarcoma, glioblastoma (such as glioblastoma multiforme) and leiomyosarcoma. Examples of other cancers that can be treated as provided herein include, but are not limited to, lymphoma, blastoma, neuroendocrine tumors, mesothelioma, schwannoma, meningioma, melanoma, and leukemia or lymphoid malignancies. Examples of such cancers include hematologic malignancies, such as Hodgkin's lymphoma; non-Hodgkin's lymphomas (Burkitt's lymphoma, small lymphocytic lymphoma/chronic lymphocytic leukemia, mycosis fungoides, mantle cell lymphoma, follicular lymphoma, diffuse large B-cell lymphoma, marginal zone lymphoma, hairy cell leukemia and lymphoplasmacytic leukemia), tumors of lymphocyte precursor cells, including B-cell acute lymphoblastic leukemia/lymphoma, and T-cell acute lymphoblastic leukemia/lymphoma, thymoma, tumors of the mature T and NK cells, including peripheral T-cell leukemias, adult T-cell leukemia/T-cell lymphomas and large granular lymphocytic leukemia, Langerhans cell histiocytosis, myeloid neoplasias such as acute myelogenous leukemias, including AML with maturation, AML without differentiation, acute promyelocytic leukemia, acute myelomonocytic leukemia, and acute monocytic leukemias, myelodysplastic syndromes, and chronic myeloproliferative disorders, including chronic myelogenous leukemia; tumors of the central nervous system such as glioma, glioblastoma, neuroblastoma, astrocytoma, medulloblastoma, ependymoma, and retinoblastoma; solid tumors of the head and neck (e.g., nasopharyngeal cancer, salivary gland carcinoma, and esophageal cancer), lung (e.g., small-cell lung cancer, non-small cell lung cancer, adenocarcinoma of the lung and squamous carcinoma of the lung), digestive system (e.g., gastric or stomach cancer including gastrointestinal cancer, cancer of the bile duct or biliary tract, colon cancer, rectal cancer, colorectal cancer, and anal carcinoma), reproductive system (e.g., testicular, penile, or prostate cancer, uterine, vaginal, vulval, cervical, ovarian, and endometrial cancer), skin (e.g., melanoma, basal cell carcinoma, squamous cell cancer, actinic keratosis, cutaneous melanoma), liver (e.g., liver cancer, hepatic carcinoma, hepatocellular cancer, and hepatoma), bone (e.g., osteoclastoma, and osteolytic bone cancers) additional tissues and organs (e.g., pancreatic cancer, bladder cancer, kidney or renal cancer, thyroid cancer, breast cancer, cancer of the peritoneum, and Kaposi's sarcoma), tumors of the vascular system (e.g., angiosarcoma and hemangiopericytoma), Wilms' tumor, retinoblastoma, osteosarcoma and Ewing's sarcoma.

2. Administration

In practicing the uses and methods herein, immunostimulatory bacteria provided herein can be administered to a subject, including a subject having a tumor or having neoplastic cells, or a subject to be immunized. One or more steps can be performed prior to, simultaneously with or after administration of the immunostimulatory bacteria to the subject including, but not limited to, diagnosing the subject with a condition appropriate for administering immunostimulatory bacteria, determining the immunocompetence of the subject, immunizing the subject, treating the subject with a chemotherapeutic agent, treating the subject with radiation, or surgically treating the subject.

For embodiments that include administering immunostimulatory bacteria to a tumor-bearing subject for therapeutic purposes, the subject typically has previously been diagnosed with a neoplastic condition. Diagnostic methods also can include determining the type of neoplastic condition, determining the stage of the neoplastic conditions, determining the size of one or more tumors in the subject, determining the presence or absence of metastatic or neoplastic cells in the lymph nodes of the subject, or determining the presence of metastases of the subject.

Some embodiments of therapeutic methods for administering immunostimulatory bacteria to a subject can include a step of determination of the size of the primary tumor or the stage of the neoplastic disease, and if the size of the primary tumor is equal to or above a threshold volume, or if the stage of the neoplastic disease is at or above a threshold stage, an immunostimulatory bacterium is administered to the subject. In a similar embodiment, if the size of the primary tumor is below a threshold volume, or if the stage of the neoplastic disease is at or below a threshold stage, the immunostimulatory bacterium is not yet administered to the subject; such methods can include monitoring the subject until the tumor size or neoplastic disease stage reaches a threshold amount, and then administering the immunostimulatory bacterium to the subject. Threshold sizes can vary according to several factors, including rate of growth of the tumor, ability of the immunostimulatory bacterium to infect a tumor, and immunocompetence of the subject. Generally the threshold size will be a size sufficient for an immunostimulatory bacterium to accumulate and replicate in or near the tumor without being completely removed by the host's immune system, and will typically also be a size sufficient to sustain a bacterial infection for a time long enough for the host to mount an immune response against the tumor cells, typically about one week or more, about ten days or more, or about two weeks or more. Exemplary threshold stages are any stage beyond the lowest stage (e.g., Stage I or equivalent), or any stage where the primary tumor is larger than a threshold size, or any stage where metastatic cells are detected.

Any mode of administration of a microorganism to a subject can be used, provided the mode of administration permits the immunostimulatory bacteria to enter a tumor or metastasis. Modes of administration can include, but are not limited to, intravenous, intraperitoneal, subcutaneous, intramuscular, topical, intratumoral, multipuncture, inhalation, intranasal, oral, intracavity (e.g., administering to the bladder via a catheter, administering to the gut by suppository or enema), aural, rectal, and ocular administration.

One skilled in the art can select any mode of administration compatible with the subject and the bacteria, and that also is likely to result in the bacteria reaching tumors and/or metastases. The route of administration can be selected by one skilled in the art according to any of a variety of factors, including the nature of the disease, the kind of tumor, and the particular bacteria contained in the pharmaceutical composition. Administration to the target site can be performed, for example, by ballistic delivery, as a colloidal dispersion system, or systemic administration can be performed by injection into an artery.

The dosage regimen can be any of a variety of methods and amounts, and can be determined by one skilled in the art according to known clinical factors. A single dose can be therapeutically effective for treating a disease or disorder in which immune stimulation effects treatment. Exemplary of such stimulation is an immune response, that includes, but is not limited to, one or both of a specific immune response and non-specific immune response, both specific and non-specific responses, innate response, primary immune response, adaptive immunity, secondary immune response, memory immune response, immune cell activation, immune cell proliferation, immune cell differentiation, and cytokine expression.

As is known in the medical arts, dosages for a subject can depend on many factors, including the subject's species, size, body surface area, age, sex, immunocompetence, and general health, the particular bacteria to be administered, duration and route of administration, the kind and stage of the disease, for example, tumor size, and other compounds such as drugs being administered concurrently. In addition to the above factors, such levels can be affected by the infectivity of the bacteria and the nature of the bacteria, as can be determined by one skilled in the art. In the present methods, appropriate minimum dosage levels of bacteria can be levels sufficient for the bacteria to survive, grow and replicate in a tumor or metastasis. Exemplary minimum levels for administering a bacterium to a 65 kg human can include at least about 5×10⁶ colony forming units (CFU), at least about 1×10⁷ CFU, at least about 5×10⁷ CFU, at least about 1×10⁸ CFU, or at least about 1×10⁹ CFU. In the present methods, appropriate maximum dosage levels of bacteria can be levels that are not toxic to the host, levels that do not cause splenomegaly of 3× or more, and/or levels that do not result in colonies or plaques in normal tissues or organs after about 1 day or after about 3 days or after about 7 days. Exemplary maximum levels for administering a bacterium to a 65 kg human can include no more than about 5×10¹¹ CFU, no more than about 1×10¹¹ CFU, no more than about 5×10¹⁰ CFU, no more than about 1×10¹⁰ CFU, or no more than about 1×10⁹ CFU.

The methods and uses provided herein can include a single administration of immunostimulatory bacteria to a subject or multiple administrations of immunostimulatory bacteria to a subject or others of a variety of regimens, including combination therapies with other anti-tumor therapeutics and/or treatments. These include, cellular therapies, such as administration of modified immune cells; CAR-T therapy; CRISPR therapy; immunotherapy, such as immune checkpoint inhibitors, such as antibodies and antibody fragments; chemotherapy and chemotherapeutic compounds, such as nucleoside analogs; surgery; oncolytic virus therapy; and radiotherapy.

The immunostimulatory bacteria, or pharmaceutical compositions containing the immunostimulatory bacteria, can be used in methods of treatment, wherein the treatment comprises combination therapy, in which a second anti-cancer agent or treatment is administered. The second anti-cancer agent or treatment is administered before, concomitantly with, after, or intermittently with, the immunostimulatory bacterium or pharmaceutical composition, and can be an immunotherapy, oncolytic virus therapy, radiation, chemotherapy, or surgery, for example. The immunotherapy can be an antibody or antibody fragment, such as an antigen-binding fragment, including an anti-PD-1, or anti-PD-L1, or anti-CTLA4, or anti-IL6, or anti-VEGF, or anti-VEGFR, or anti-VEGFR2 antibody, or fragments thereof.

In some embodiments, a single administration is sufficient to establish immunostimulatory bacteria in a tumor, where the bacteria can colonize and can cause or enhance an anti-tumor response in the subject. In other embodiments, the immunostimulatory bacteria provided for use in the methods herein can be administered on different occasions, separated in time typically by at least one day. Separate administrations can increase the likelihood of delivering a bacterium to a tumor or metastasis, where a previous administration may have been ineffective in delivering the bacterium to a tumor or metastasis. In embodiments, separate administrations can increase the locations on a tumor or metastasis where bacterial colonization/proliferation can occur or can otherwise increase the titer of bacteria accumulated in the tumor, which can increase eliciting or enhancing a host's anti-tumor immune response.

When separate administrations are performed, each administration can be a dosage amount that is the same or different relative to other administration dosage amounts. In one embodiment, all administration dosage amounts are the same. In other embodiments, a first dosage amount can be a larger dosage amount than one or more subsequent dosage amounts, for example, at least 10× larger, at least 100× larger, or at least 1000× larger than subsequent dosage amounts. In one example of a method of separate administrations in which the first dosage amount is greater than one or more subsequent dosage amounts, all subsequent dosage amounts can be the same, smaller amount relative to the first administration.

Separate administrations can include any number of two or more administrations, including two, three, four, five or six administrations. One skilled in the art readily can determine the number of administrations to perform, or the desirability of performing one or more additional administrations, according to methods known in the art for monitoring therapeutic methods and other monitoring methods provided herein. Accordingly, the methods provided herein include methods of providing to the subject one or more administrations of immunostimulatory bacteria, where the number of administrations can be determined by monitoring the subject, and, based on the results of the monitoring, determining whether or not to provide one or more additional administrations. Deciding whether or not to provide one or more additional administrations can be based on a variety of monitoring results, including, but not limited to, indication of tumor growth or inhibition of tumor growth, appearance of new metastases or inhibition of metastasis, the subject's anti-bacterial antibody titer, the subject's anti-tumor antibody titer, the overall health of the subject and the weight of the subject.

The time period between administrations can be any of a variety of time periods. The time period between administrations can be a function of any of a variety of factors, including monitoring steps, as described in relation to the number of administrations, the time period for a subject to mount an immune response, the time period for a subject to clear bacteria from normal tissue, or the time period for bacterial colonization/proliferation in the tumor or metastasis. In one example, the time period can be a function of the time period for a subject to mount an immune response; for example, the time period can be more than the time period for a subject to mount an immune response, such as more than about one week, more than about ten days, more than about two weeks, or more than about a month; in another example, the time period can be less than the time period for a subject to mount an immune response, such as less than about one week, less than about ten days, less than about two weeks, or less than about a month. In another example, the time period can be a function of the time period for bacterial colonization/proliferation in the tumor or metastasis; for example, the time period can be more than the amount of time for a detectable signal to arise in a tumor or metastasis after administration of a microorganism expressing a detectable marker, such as about 3 days, about 5 days, about a week, about ten days, about two weeks, or about a month.

The methods used herein also can be performed by administering compositions, such as suspensions and other formulations, containing the immunostimulatory bacteria provided herein. Such compositions contain the bacteria and a pharmaceutically acceptable excipient or vehicle, as provided herein or known to those of skill in the art.

As discussed above, the uses and methods provided herein also can include administering one or more therapeutic compounds, such as anti-tumor compounds or other cancer therapeutics, to a subject in addition to administering immunostimulatory bacteria to the subject. The therapeutic compounds can act independently, or in conjunction with the immunostimulatory bacteria, for tumor therapeutic effects. Therapeutic compounds that can act independently include any of a variety of known chemotherapeutic compounds that can inhibit tumor growth, inhibit metastasis growth and/or formation, decrease the size of a tumor or metastasis, or eliminate a tumor or metastasis, without reducing the ability of the immunostimulatory bacteria to accumulate in a tumor, replicate in the tumor, and cause or enhance an anti-tumor immune response in the subject. Examples of such chemotherapeutic agents include, but are not limited to, alkylating agents such as thiotepa and cyclosphosphamide; alkyl sulfonates such as busulfan, improsulfan and piposulfan; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, and testolactone; anti-adrenals such as aminoglutethimide, mitotane, and trilostane; anti-androgens such as flutamide, nilutamide, bicalutamide, leuprolide, and goserelin; antibiotics such as aclacinomycins, actinomycin, anthramycin, azaserine, bleomycins, cactinomycin, calicheamicin, carubicin, carminomycin, carzinophilin, chromomycins, dactinomycin, daunorubicin, detorubicin, 6-diazo-5-oxo-L-norleucine, doxorubicin, epirubicin, esorubicin, idarubicin, marcellomycin, mitomycins, mycophenolic acid, nogalamycin, olivomycins, peplomycin, porfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, and zorubicin; anti estrogens including for example tamoxifen, raloxifene, aromatase inhibiting 4(5)-imidazoles, 4-hydroxytamoxifen, trioxifene, keoxifene, LY 117018, onapristone, and toremifene (Fareston); anti-metabolites such as methotrexate and 5-fluorouracil (5-FU); folic acid analogues such as denopterin, methotrexate, pteropterin, and trimetrexate; aziridines such as benzodepa, carboquone, meturedepa, and uredepa; ethylenimines and methylmelamines including altretamine, triethylenemelamine, triethylenephosphoramide, triethylenethiophosphoramide and trimethylol melamine; folic acid replenisher such as folinic acid; nitrogen mustards such as chlorambucil, chlornaphazine, chlorophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, and uracil mustard; nitrosoureas such as carmustine, chlorozotocin, fotemustine, lomustine, nimustine, and ranimustine; platinum analogs such as cisplatin and carboplatin; vinblastine; platinum; proteins such as arginine deiminase and asparaginase; purine analogs such as fludarabine, 6-mercaptopurine, thiamiprine, and thioguanine; pyrimidine analogs such as ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine, and 5-FU; taxanes, such as paclitaxel and docetaxel and albuminated forms thereof (i.e., nab-paclitaxel and nab-docetaxel), topoisomerase inhibitor RFS 2000; thymidylate synthase inhibitor (such as Tomudex); and additional chemotherapeutics including aceglatone; aldophosphamide glycoside; aminolevulinic acid; amsacrine; bestrabucil; bisantrene; edatrexate; defosfamide; demecolcine; diaziquone; difluoromethylornithine (DFMO); eflornithine; elliptinium acetate; etoglucid; gallium nitrate; hydroxyurea; lentinan; lonidamine; mitoguazone; mitoxantrone; mopidamol; nitracrine; pentostatin; phenamet; pirarubicin; podophyllinic acid; 2-ethylhydrazide; procarbazine; PSK®; razoxane; sizofiran; spirogermanium; tenuazonic acid; triaziquone; 2,2′, 2″-trichlorotriethylamine; urethan; vindesine; dacarbazine; mannomustine; mitobronitol; mitolactol; pipobroman; gacytosine; arabinoside (“Ara-C”); cyclophosphamide; thiotepa; chlorambucil; gemcitabine; 6-thioguanine; mercaptopurine; methotrexate; etoposide (VP-16); ifosfamide; mitomycin C; mitoxantrone; vincristine; vinorelbine; Navelbine; Novantrone; teniposide; daunomycin; aminopterin; Xeloda; ibandronate; CPT-11; retinoic acid; esperamycins; capecitabine; and topoisomerase inhibitors such as irinotecan. Pharmaceutically acceptable salts, acids or derivatives of any of the above can also be used.

Therapeutic compounds that act in conjunction with the immunostimulatory bacteria include, for example, compounds that increase the immune response eliciting properties of the bacteria, e.g., by increasing expression of the RNAi, such as shRNA and miRNA, that inhibit, suppress or disrupt expression of the checkpoint genes, such as PD-L1, or TREX1 or other checkpoint genes, or compounds that can further augment bacterial colonization/proliferation. For example, a gene expression-altering compound can induce or increase transcription of a gene in a bacterium, such as an exogenous gene, e.g., encoding shRNA that inhibit, suppress or disrupt expression of one or more checkpoint genes, thereby provoking an immune response. Any of a wide variety of compounds that can alter gene expression are known in the art, including IPTG and RU486. Exemplary genes whose expression can be up-regulated include proteins and RNA molecules, including toxins, enzymes that can convert a prodrug to an anti-tumor drug, cytokines, transcription regulating proteins, shRNA, siRNA, and ribozymes. In other embodiments, therapeutic compounds that can act in conjunction with the immunostimulatory bacteria to increase the colonization/proliferation or immune response eliciting properties of the bacteria are compounds that can interact with a bacteria-expressed gene product, and such interaction can result in an increased killing of tumor cells or an increased anti-tumor immune response in the subject. A therapeutic compound that can interact with a bacteria-expressed gene product can include, for example a prodrug or other compound that has little or no toxicity or other biological activity in its subject-administered form, but after interaction with a bacteria-expressed gene product, the compound can develop a property that results in tumor cell death, including but not limited to, cytotoxicity, ability to induce apoptosis, or ability to trigger an immune response. A variety of prodrug-like substances are known in the art, including ganciclovir, 5-fluorouracil, 6-methylpurine deoxyriboside, cephalosporin-doxorubicin, 4-[(2-chloroethyl)(2-mesuloxyethyl)amino]benzoyl-L-glutamic acid, acetaminophen, indole-3-acetic acid, CB1954, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycampotothecin, bis-(2-chloroethyl)amino-4-hydroxyphenylaminomethanone 28, 1-chloromethyl-5-hydroxy-1,2-dihyro-3H-benz[e]indole, epirubicin glucuronide, 5′-deoxy5-fluorouridine, cytosine arabinoside, and linamarin.

3. Monitoring

The methods provided herein can further include one or more steps of monitoring the subject, monitoring the tumor, and/or monitoring the immunostimulatory bacteria administered to the subject. Any of a variety of monitoring steps can be included in the methods provided herein, including, but not limited to, monitoring tumor size, monitoring the presence and/or size of metastases, monitoring the subject's lymph nodes, monitoring the subject's weight or other health indicators including blood or urine markers, monitoring anti-bacterial antibody titer, monitoring bacterial expression of a detectable gene product, and directly monitoring bacterial titer in a tumor, tissue or organ of a subject.

The purpose of the monitoring can be simply for assessing the health state of the subject or the progress of therapeutic treatment of the subject, or can be for determining whether or not further administration of the same or a different immunostimulatory bacterium is warranted, or for determining when or whether or not to administer a compound to the subject where the compound can act to increase the efficacy of the therapeutic method, or the compound can act to decrease the pathogenicity of the bacteria administered to the subject.

In some embodiments, the methods provided herein can include monitoring one or more bacterially expressed genes. Bacteria, such as those provided herein or otherwise known in the art, can express one or more detectable gene products, including but not limited to, detectable proteins.

As provided herein, measurement of a detectable gene product expressed in a bacterium can provide an accurate determination of the level of bacteria present in the subject. As further provided herein, measurement of the location of the detectable gene product, for example, by imaging methods including tomographic methods, can determine the localization of the bacteria in the subject. Accordingly, the methods provided herein that include monitoring a detectable bacterial gene product can be used to determine the presence or absence of the bacteria in one or more organs or tissues of a subject, and/or the presence or absence of the bacteria in a tumor or metastases of a subject. Further, the methods provided herein that include monitoring a detectable bacterial gene product can be used to determine the titer of bacteria present in one or more organs, tissues, tumors or metastases. Methods that include monitoring the localization and/or titer of bacteria in a subject can be used for determining the pathogenicity of bacteria since bacterial infection, and particularly the level of infection, of normal tissues and organs can indicate the pathogenicity of the bacteria. The methods that include monitoring the localization and/or titer of immunostimulatory bacteria in a subject can be performed at multiple time points and, accordingly, can determine the rate of bacterial replication in a subject, including the rate of bacterial replication in one or more organs or tissues of a subject; accordingly, methods that include monitoring a bacterial gene product can be used for determining the replication competence of the bacteria. The methods provided herein also can be used to quantitate the amount of immunostimulatory bacteria present in a variety of organs or tissues, and tumors or metastases, and can thereby indicate the degree of preferential accumulation of the bacteria in a subject; accordingly, the bacterial gene product monitoring can be used in methods of determining the ability of the bacteria to accumulate in tumor or metastases in preference to normal tissues or organs. Since the immunostimulatory bacteria used in the methods provided herein can accumulate in an entire tumor or can accumulate at multiple sites in a tumor, and can also accumulate in metastases, the methods provided herein for monitoring a bacterial gene product can be used to determine the size of a tumor or the number of metastases present in a subject. Monitoring such presence of bacterial gene product in a tumor or metastasis over a range of time can be used to assess changes in the tumor or metastases, including growth or shrinking of a tumor, or development of new metastases or disappearance of metastases, and also can be used to determine the rate of growth or shrinking of a tumor, or development of new metastases or disappearance of metastases, or the change in the rate of growth or shrinking of a tumor, or development of new metastases or disappearance of metastases. Accordingly, monitoring a bacterial gene product can be used for monitoring a neoplastic disease in a subject, or for determining the efficacy of treatment of a neoplastic disease, by determining rate of growth or shrinking of a tumor, or development of new metastases or disappearance of metastases, or the change in the rate of growth or shrinking of a tumor, or development of new metastases or disappearance of metastases.

Any of a variety of detectable proteins can be detected by monitoring, exemplary of which are any of a variety of fluorescence proteins (e.g., green fluorescence proteins), any of a variety of luciferases, transferrin or other iron binding proteins; or receptors, binding proteins, and antibodies, where a compound that specifically binds the receptor, binding protein or antibody can be a detectable agent or can be labeled with a detectable substance (e.g., a radionuclide or imaging agent).

Tumor and/or metastasis size can be monitored by any of a variety of methods known in the art, including external assessment methods or tomographic or magnetic imaging methods. In addition to the methods known in the art, methods provided herein, for example, monitoring bacterial gene expression, can be used for monitoring tumor and/or metastasis size.

Monitoring size over several time points can provide information regarding the increase or decrease in size of a tumor or metastasis, and can also provide information regarding the presence of additional tumors and/or metastases in the subject. Monitoring tumor size over several time points can provide information regarding the development of a neoplastic disease in a subject, including the efficacy of treatment of a neoplastic disease in a subject.

The methods provided herein also can include monitoring the antibody titer in a subject, including antibodies produced in response to administration of immunostimulatory bacteria to a subject. The bacteria administered in the methods provided herein can elicit an immune response to endogenous bacterial antigens. The bacteria administered in the methods provided herein also can elicit an immune response to exogenous genes expressed by the bacteria. The bacteria administered in the methods provided herein also can elicit an immune response to tumor antigens. Monitoring antibody titer against bacterial antigens, bacterially expressed exogenous gene products, or tumor antigens can be used to monitor the toxicity of the bacteria, the efficacy of treatment methods, or the level of gene product or antibodies for production and/or harvesting.

Monitoring antibody titer can be used to monitor the toxicity of the bacteria. Antibody titer against a bacteria can vary over the time period after administration of the bacteria to the subject, where at some particular time points, a low anti-(bacterial antigen) antibody titer can indicate a higher toxicity, while at other time points a high anti-(bacterial antigen) antibody titer can indicate a higher toxicity. The bacteria used in the methods provided herein can be immunogenic, and can, therefore, elicit an immune response soon after administering the bacteria to the subject. Generally, immunostimulatory bacteria against which the immune system of a subject can mount a strong immune response can be bacteria that have low toxicity when the subject's immune system can remove the bacteria from all normal organs or tissues. Thus, in some embodiments, a high antibody titer against bacterial antigens soon after administering the bacteria to a subject can indicate low toxicity of the bacteria.

In other embodiments, monitoring antibody titer can be used to monitor the efficacy of treatment methods. In the methods provided herein, antibody titer, such as anti-(tumor antigen) antibody titer, can indicate the efficacy of a therapeutic method such as a therapeutic method to treat neoplastic disease. Therapeutic methods provided herein can include causing or enhancing an immune response against a tumor and/or metastasis. Thus, by monitoring the anti-(tumor antigen) antibody titer, it is possible to monitor the efficacy of a therapeutic method in causing or enhancing an immune response against a tumor and/or metastasis.

In other embodiments, monitoring antibody titer can be used for monitoring the level of gene product or antibodies for production and/or harvesting. As provided herein, methods can be used for producing proteins, RNA molecules or other compounds, particularly RNA molecules such as shRNA, by expressing an exogenous gene in a microorganism that has accumulated in a tumor. Monitoring antibody titer against the protein, RNA molecule or other compound can indicate the level of production of the protein, RNA molecule or other compound by the tumor-accumulated microorganism, and also can directly indicate the level of antibodies specific for such a protein, RNA molecule or other compound.

The methods provided herein also can include methods of monitoring the health of a subject. Some of the methods provided herein are therapeutic methods, including neoplastic disease therapeutic methods. Monitoring the health of a subject can be used to determine the efficacy of the therapeutic method, as is known in the art. The methods provided herein also can include a step of administering to a subject an immunostimulatory bacterium, as provided herein. Monitoring the health of a subject can be used to determine the pathogenicity of an immunostimulatory bacterium administered to a subject. Any of a variety of health diagnostic methods for monitoring disease such as neoplastic disease, infectious disease, or immune-related disease can be monitored, as is known in the art. For example, the weight, blood pressure, pulse, breathing, color, temperature or other observable state of a subject can indicate the health of a subject. In addition, the presence or absence or level of one or more components in a sample from a subject can indicate the health of a subject. Typical samples can include blood and urine samples, where the presence or absence or level of one or more components can be determined by performing, for example, a blood panel or a urine panel diagnostic test. Exemplary components indicative of a subject's health include, but are not limited to, white blood cell count, hematocrit, and c-reactive protein concentration.

The methods provided herein can include monitoring a therapy, where therapeutic decisions can be based on the results of the monitoring. Therapeutic methods provided herein can include administering to a subject immunostimulatory bacteria, where the bacteria can preferentially accumulate in a tumor and/or metastasis, and where the bacteria can cause or enhance an anti-tumor immune response. Such therapeutic methods can include a variety of steps including multiple administrations of a particular immunostimulatory bacterium, administration of a second immunostimulatory bacterium, or administration of a therapeutic compound. Determination of the amount, timing or type of immunostimulatory bacteria or compound to administer to the subject can be based on one or more results from monitoring the subject. For example, the antibody titer in a subject can be used to determine whether or not it is desirable to administer an immunostimulatory bacterium and, optionally, a compound, the quantity of bacteria and/or compound to administer, and the type of bacteria and/or compound to administer, where, for example, a low antibody titer can indicate the desirability of administering an additional immunostimulatory bacterium, a different immunostimulatory bacterium, and/or a therapeutic compound such as a compound that induces bacterial gene expression or a therapeutic compound that is effective independent of the immunostimulatory bacteria.

In another example, the overall health state of a subject can be used to determine whether or not it is desirable to administer an immunostimulatory bacterium and, optionally, a compound, the quantity of bacterium or compound to administer, and the type of bacterium and/or compound to administer where, for example, determining that the subject is healthy can indicate the desirability of administering additional bacteria, different bacteria, or a therapeutic compound such as a compound that induces bacterial gene (e.g., shRNA that inhibits one or more checkpoint gene(s)) expression. In another example, monitoring a detectable bacterially expressed gene product can be used to determine whether it is desirable to administer an immunostimulatory bacterium and, optionally, a compound, the quantity of bacterium and/or compound to administer, and the type of bacterium and/or compound to administer where, for example, determining that the subject is healthy can indicate the desirability of administering additional bacteria, different bacteria, or a therapeutic compound such as a compound that induces bacterial gene (e.g., shRNA that inhibits one or more checkpoint gene(s)) expression. Such monitoring methods can be used to determine whether or not the therapeutic method is effective, whether or not the therapeutic method is pathogenic to the subject, whether or not the bacteria have accumulated in a tumor or metastasis, and whether or not the bacteria have accumulated in normal tissues or organs. Based on such determinations, the desirability and form of further therapeutic methods can be derived.

In another example, monitoring can determine whether or not immunostimulatory bacteria have accumulated in a tumor or metastasis of a subject. Upon such a determination, a decision can be made to further administer additional bacteria, a different immunostimulatory bacterium and, optionally, a compound to the subject.

J. EXAMPLES

The following examples are included for illustrative purposes only and are not intended to limit the scope of the invention.

Summary of Some Exemplary Engineered Immunostimulatory Bacterial Strains and Nomenclature:

Strain Strain # Plasmid Background RNAi Targets Alternate name AST-100 None YS1646 none VNP 20009 AST-101 None YS1646-ASD none ASD (asd gene knockout) AST-102 pEQU6 YS1646 none YS1646 (pEQU6-plasmid) AST-103 pEQU6 YS1646 Scrambled YS1646 (pEQU6-shSCR) (shRNA) AST-104 pEQU6 YS1646 muTREX1 YS1646 (pEQU6-shTREX1) (shRNA) ARI-108 AST-105 pEQU6 YS1646 muPD-L1 YS1646 (pEQU6-shPDL1) (shRNA) ARI-115 AST-106 pEQU6 YS1646 muTREX1 YS1646 (pEQU6-miTREX1) (microRNA) ARI-203 AST-107 pATI-U6 YS1646-ASD Scrambled ASD (pATI-shSCR) (shRNA) AST-108 pATI-U6 YS1646-ASD muTREX1 ASD (pATI-shTREX1) (shRNA) ARI-108 AST-109 pATIKAN-U6 YS1646-ASD Scrambled ASD (pATIKan-shSCR) (shRNA) AST-110 pATIKAN-U6 YS1646-ASD muTREX1 ASD (pATIKan-shTREX1) (shRNA) ARI-108 AST-111 None YS1646-ASD- None ASD/FLG (asd and flagellin knockout) fljb-fliC AST-112 pATI-U6 YS1646-ASD- muTREX1 ASD/FLG (pATI-shTREX1) fljb-fliC (shRNA) ARI-108 AST-113 pATI-U6 YS1646-ASD- muTREX1 ASD/FLG (pATI-U6 Kan fljb-fliC (shRNA) shTREX1) ARI-108 AST-114 None YS1646-ASD- None ASD/LLO (asd knockout/ LLO cytoLLO knock-in) AST-115 pATI-U6 YS1646-ASD- muTREX1 ASD/LLO (pATIKan-shTREX1) LLO (shRNA) ARI-108 AST-116 pATIKanpBRori-U6 YS1646-ASD Scrambled ASD (pATIKanLow-shSCR) AST-117 pATIKanpBRori-U6 YS1646-ASD muTREX1 ASD (pATIKanLow-shTREX1) (shRNA) ARI-108 AST-118 pATIKanpBRori-U6 YS1646-ASD- muTREX1 ASD/FLG (pATIKanLow-shTREX1) fljb-fliC (shRNA) ARI-108 AST-119 pATIKanpBRori-U6 YS1646-ASD- muTREX1 ASD/LLO (pATIKanLow-shTREX1) pMTL-LLO (shRNA) ARI-108 AST-120 pEQU6 YS1646-ASD- muTREX1 ASD/LLO (pEQU6-miTREX1) pMTL-LLO (microRNA) Suicidal ARI-203 AST-121 pEQU6 YS1646 muVISTA YS1646 (pEQU6-shVISTA) ARI-157 AST-122 pEQU6 YS1646 muTGF-beta YS1646 (pEQU6-TGF-beta) ARI-149 AST-123 pEQU6 YS1645 muBeta-Catenin YS1646 (pEQU6-Beta-Catenin) ARI-166

It is understood that these strains are listed for reference, the same deletions and insertions can be effected in a wild-type Salmonella typhimurium strain, such as the strain deposited under ATCC accession #14028, or a strain having all of the identifying characteristics thereof. The wild-type strain can additionally be made auxotrophic for adenosine by appropriate selection or deletions. The construction of and use of these strains is described in Published International PCT Application No. WO 2019/014398, and in U.S. Application Publication No. 2019/0017050.

Example 1 Salmonella asd Gene Knockout Strain Engineering

Strain AST-101 was prepared. It is an attenuated Salmonella typhimurium strain derived from strain YS1646 (which can be purchased from ATCC, Catalog #202165) that has been engineered to be asd⁻ (an asd gene knockout). In this example, the Salmonella typhimurium strain YS1646 asd⁻ gene deletion was engineered using modifications of the method of Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645 (2000)) as outlined in FIG. 1 , and described below. The methods and resulting products in this example and all examples below can be used with other starting bacteria, such as wild-type Salmonella typhimurium, such as the strain deposited under ATCC accession #14028.

Introduction of the Lambda Red Helper Plasmid into YS1646

The YS1646 strain was prepared to be electrocompetent as described previously (Sambrook J., (1998) Molecular Cloning, A Laboratory Manual, 2nd Ed. Cold Spring Harbor, N.Y. Cold Spring Harbor Laboratory) by growing a culture in LB and concentrating 100-fold and washing three times with ice-cold 10% glycerol. The electrocompetent strain was electroporated with the Lambda red helper plasmid pKD46 (SEQ ID NO:218) using a 0.2 cm gap cuvette at the following settings: 2.5 kV, 186 ohms, 50 μF. Transformants carrying pKD46 were grown in 5 mL SOC medium with ampicillin and 1 mM L-arabinose at 30° C. and selected on LB agar plates containing ampicillin. A YS1646 clone containing the lambda red helper plasmid pKD46 then was made electrocompetent, as described above for YS1646.

Construction of asd Gene Knockout Cassette

The asd gene from the genome of YS1646 (Broadway et al. (2014) J. Biotechnology 192:177-178) was used for designing the asd gene knockout cassette. A plasmid containing 204 and 203 bp of homology to the left hand and right hand regions, respectively, of the asd gene, was transformed into DH5-alpha competent cells. A kanamycin gene cassette flanked by lox P sites was cloned into this plasmid. The asd gene knockout cassette then was PCR amplified using primers asd−1 and asd−2 (Table 1) and gel purified.

Execution of asd Gene Deletion

The YS1646 strain carrying plasmid pKD46 was electroporated with the gel-purified linear asd gene knock-out cassette. Electroporated cells were recovered in SOC medium and plated onto LB Agar plates supplemented with Kanamycin (20 μg/mL) and diaminopimelic acid (DAP, 50 μg/ml). During this step, lambda red recombinase induces homologous recombination of the chromosomal asd gene with the kan cassette (due to the presence of homologous flanking sequences upstream and downstream of the chromosomal asd gene), and knockout of the chromosomal copy of the asd gene occurs. The presence of the disrupted asd gene in the selected kanamycin resistant clones was confirmed by PCR amplification with primers from the YS1646 genome flanking the sites of disruption (primer asd-3) and from the multi-cloning site (primer scFv-3) (Table 1). Colonies were also replica plated onto LB plates with and without supplemental DAP to demonstrate DAP auxotrophy. All clones with the asd gene deletion were unable to grow in the absence of supplemental DAP, demonstrating DAP auxotrophy.

TABLE 1 Primer information Primer SEQ name Primer sequence ID NO. asd-1 ccttcctaacgcaaattccctg 219 asd-2 ccaatgctctgcttaactcctg 220 asd-3 gcctcgccatgtttcagtacg 221 asd-4 ggtctggtgcattccgagtac 222 scFv-3 cataatctgggtccttggtctgc 223 Kanamycin Gene Cassette Removal

The kan selectable marker was removed by using the Cre/loxP site-specific recombination system. The YS1646 asd⁻ gene Kan^(R) mutant was transformed with pJW168 (a temperature sensitive plasmid expressing the cre recombinase, SEQ ID NO:224). Amp^(R) colonies were selected at 30° C.; pJW168 was subsequently eliminated by growth at 42° C. A selected clone (AST-101) then was tested for loss of kan by replica plating on LB agar plates with and without kanamycin, and confirmed by PCR verification using primers from YS1646 genome flanking the sites of disruption (primer asd-3 and asd-4, for primer sequence, see Table 1).

Characterization of the asd Deletion Mutant Strain AST-101

The asd mutant AST-101 was unable to grow on LB agar plates at 37° C., but was able to grow on LB plates containing 50 μg/mL diaminopimelic acid (DAP). The asd mutant growth rate was evaluated in LB liquid media and it was unable to grow in liquid LB but was able to grow in LB supplemented with 50 μg/mL DAP, as determined by measuring absorbance at 600 nM.

Sequence Confirmation of the AST-101 asd Locus Sequence after asd Gene Deletion

The AST-101 asd gene deletion strain was verified by DNA sequencing using primers asd-3 and asd-4. Sequencing of the region flanking the asd locus was performed and the sequence confirmed that the asd gene was deleted from the YS1646 chromosome.

Example 2 Generation of Modified Salmonella typhimurium Strains from Wild-Type Salmonella typhimurium

The purI, msbB and asd genes were individually deleted from the genome of wild-type Salmonella typhimurium strain ATCC 14028 using the lambda-derived Red recombination system as described in Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645 (2000)), to generate a base-strain designated 14028:ΔpurI/ΔmsbB/Δasd. The flagellin genes fljB and fliC were subsequently deleted to generate the strain 14028:ΔpurI/ΔmsbB/Δasd/ΔfljB/ΔfliC, and the pagP gene was then deleted to generate the strain 14028: ΔpurI/ΔmsbB/Δasd/ΔfljB/ΔfliC/ΔpagP. Strains 14028:ΔpurI/ΔmsbB/Δasd/ΔfljB/ΔfliC and 14028:ΔpurI/ΔmsbB/Δasd/ΔfljB/ΔfliC/ΔpagP were electroporated with a plasmid containing a functional asd gene, to complement the chromosomal deletion of asd and ensure plasmid maintenance in vivo, and a eukaryotic expression cassette encoding the red fluorescent protein mCherry under control of the EF1-α promoter.

Example 3 Modified Salmonella typhimurium Targets Demonstrate Robust Tumor Growth Inhibition in Multiple Syngeneic Murine Tumor Models

PD-L1

The immune system has evolved several checks and balances to limit autoimmunity. Programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) are two examples of numerous inhibitory “immune checkpoints,” which function by downregulating immune responses. The binding of PD-L1 to PD-1 interferes with CD8⁺ T cell signaling pathways, impairing the proliferation and effector function of CD8⁺ T cells, and inducing T cell tolerance (Topalian et al. (2012) N. Engl. J. Med. 366:2443-2454).

Tumor colonization of a modified Salmonella typhimurium strain delivering shRNA to knockdown the PD-L1 gene disrupts its binding to PD-1, and its inhibition of CD8⁺ T cell function. PD-L1/PD-1 checkpoint inhibition synergizes well with the immunostimulatory S. typhimurium containing CpG plasmid DNA, all in one therapeutic modality. In place of an RNAi, the immunostimulatory bacterium can be modified to encode an antigen-binding fragment or single chain antibody that inhibits PD-L1 or PD-1, to inhibit the PD-1 pathway.

To demonstrate the in vivo efficacy of the YS1646 strain containing a plasmid encoding shRNA against PD-L1 (AST-105), or other inhibitor of PD-L1 or the PD-1 pathway, this strain, in comparison to the AST-102 strain (containing a control plasmid that also contains CpG motifs) was evaluated in a murine colon carcinoma model. For this experiment, 6-8 week-old female BALB/c mice (10 mice per group) were inoculated SC in the right flank with CT26 murine colon carcinoma (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were intravenously (IV) injected twice, four days apart, with 5×10⁶ CFUs of AST-105 or AST-102, or were IV administered an anti-PD-L1 antibody (4 mg/kg, BioXCell clone 10F.9G2). Six hours following the first IV dose, mice were bled, and plasma was collected and assessed for pro-inflammatory cytokines using the Mouse Inflammation Cytometric Bead Array kit and analyzed by FACS (BD Biosciences).

Treatment with strain AST-105 demonstrated statistically significant tumor control compared to treatment with the plasmid-containing control strain AST-102 (69% TGI, p=0.05, day 25). Tumor growth inhibition was also greater for treatment with AST-105 (expressing shPD-L1) than from systemic administration of an anti-PD-L1 antibody (68% TGI vs. anti-PD-L1).

Comparing the production of innate pro-inflammatory cytokines at 6 hours post IV injection, the cytokines elicited by strain AST-105 were significantly higher compared to the anti-PD-L1 antibody (p<0.05), and much higher than those from AST-102. These data demonstrate that inhibiting PD-L1 within the tumor microenvironment, compared to systemic administration of anti-PD-L1 antibody, uniquely activates potent pro-inflammatory cytokines that induce anti-tumor immunity and promote tumor growth inhibition in a murine model of colon carcinoma.

Example 4 Intratumoral Administration of Modified S. typhimurium Shtrex1 Provides Distal Tumor Colonization and Complete Anti-Tumor Responses in a Dual Flank Murine Colon Carcinoma Model

A hallmark of inducing adaptive immunity to a tumor is the ability to induce regression of a distal, untreated tumor. To assess the ability of the YS1646 strain containing the pEQU6 shRNA plasmids to induce primary and distal tumor growth inhibition in a dual flank murine colon carcinoma model, 6-8 week-old female BALB/c mice (10 mice per group) were inoculated SC in the right and left flanks with CT26 murine colon carcinoma (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were intratumorally (IT) injected twice, four days apart, into the right flank tumor with 5×10⁶ CFUs of AST-104, (pEQU6 shTREX1 in YS1646), AST-105 (pEQU6 shPD-L1 in YS1646) or AST-102 (plasmid control in YS1646), and compared to PBS control.

IT injection of AST-104 and AST-105 induced significant tumor growth inhibition in the injected tumor, compared to the PBS control (AST-105-60.5% TGI, p=0.03; AST-104-61.4% TGI, p=0.03 day 25). Unlike AST-105, only AST-104 induced significant growth inhibition of the distal, untreated tumor compared to PBS (60% TGI, p<0.0001, day 25), and significant distal tumor growth inhibition compared to AST-102 containing the plasmid control (p=0.004, day 25). The AST-104 strain also demonstrated significant tumor regression and increased survival compared to PBS control (p=0.0076, Log-rank (Mantel-Cox) test) with 2/10 complete remissions.

To determine whether the bacteria colonize injected, as well as distal tumors, tumor-bearing mice treated with AST-104 were sacrificed and tumors were collected. Injected and distal tumors were transferred to M tubes and were homogenized in PBS using a gentleMACS™ Dissociator (Miltenyi Biotec). Tumor homogenates were serially diluted and plated on LB agar plates and incubated at 37° C. for colony forming unit (CFU) determination. As shown in FIG. 2 , the distal tumor was colonized to the same extent as the injected tumor, indicating that the engineered Salmonella strains dosed with an intratumoral route of administration are able to transit and colonize distal lesions. These data demonstrate the potency of administering an immunostimulatory bacteria intratumorally with the ability to systemically colonize distal tumor lesions preferentially over other organs, and the potency of activating the STING Type I Interferon pathway, leading to systemic tumor regression and complete remission.

Example 5 Modified S. typhimurium Strains with Plasmids Containing CpG Elements Demonstrate Enhanced Anti-Tumor Activity Compared To YS1646 Parental Strain

Toll-like receptors (TLRs) are key receptors for sensing pathogen-associated molecular patterns (PAMPs) and activating innate immunity against pathogens (Akira et al. (2001) Nat. Immunol. 2(8):675-680). Of these, TLR9 is responsible for recognizing hypomethylated CpG motifs in pathogenic DNA which do not occur naturally in mammalian DNA (McKelvey et al. (2011) J. Autoimmunity 36:76). Recognition of CpG motifs upon phagocytosis of pathogens into endosomes in immune cell subsets induces IFR7-dependent type I interferon signaling and activates innate and adaptive immunity. It is shown herein, that the S. typhimurium strain YS1646 carrying modified Salmonella typhimurium plasmids containing CpG motifs (YS1646 pEQU6 Scramble) similarly activate TLR9 and induce type I IFN-mediated innate and adaptive immunity, as compared to the YS1646 strain without a plasmid.

The CpG motifs in the engineered plasmids used here are shown in Table 2. The pEQU6 shSCR (non-cognate shRNA) plasmid in strain AST-103 possesses 362 CpG motifs, indicating that Salmonella-based plasmid delivery can be immuno-stimulatory and have an anti-tumor effect, when compared to the same Salmonella lacking transformation with this plasmid. To assess the ability of CpG-containing plasmids within YS1646 to induce tumor growth inhibition in a murine colon carcinoma model, 6-8 week-old female BALB/c mice (9 mice per group) were inoculated subcutaneously (SC) in the right flank with CT26 (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected weekly with three doses of 5×10⁶ CFUs of YS1646 (AST-100) or YS1646 containing an shRNA scrambled plasmid with CpG motifs (AST-103), and compared to PBS control.

TABLE 2 CpG motifs in the engineered plasmids Number SEQ of CpG ID Sequence name Motifs NO. pBR322 Origin 80 243 pEQU6 (shSCR) 362 244 Asd Gene ORF 234 242 pATI-2.0 538 245

As shown in FIG. 3 , the YS1646 (AST-100) strain demonstrated modest tumor control (32% TGI, p=ns, day 28) as compared to PBS. The AST-103 strain, that varies from YS1646 only by the addition of the CpG-containing plasmid encoding a non-cognate scrambled shRNA, demonstrated highly significant tumor growth inhibition compared to YS1646 alone, untransformed and therefore lacking a plasmid (p=0.004, day 32).

The asd gene possesses 234 CpG motifs (Table 2), indicating that a plasmid containing it can have immunostimulatory properties. As shown in FIG. 16 , AST-109 (YS1646-ASD with scrambled shRNA) had 51% tumor growth inhibition vs PBS alone, indicative of a strong immuno-stimulatory effect.

These data demonstrate the potent immunostimulatory properties of plasmid DNA containing TLR9-activating CpG motifs within a tumor-targeting attenuated strain of S. typhimurium.

Example 6 Vector Synthesis

Complementation of asd Deletion by asd Expression from Plasmids

A plasmid (pATIU6) was chemically synthesized and assembled (SEQ ID NO:225). The plasmid contained the following features: a high copy (pUC19) origin of replication, a U6 promoter for driving expression of a short hairpin, an ampicillin resistance gene flanked by HindIII restriction sites for subsequent removal, and the asd gene containing 85 base pairs of sequence upstream of the start codon (SEQ ID NO:246). Into this vector, shRNAs targeting murine TREX1 or a scrambled, non-cognate shRNA sequence were introduced by restriction digestion with SpeI and XhoI and ligation and cloning into E. coli DH5-alpha. The resulting plasmids, designated pATI-shTREX1 and pATI-shSCR, respectively, were amplified in E. coli and purified for transformation into the asd knockout strain AST-101 by electroporation and clonal selection on LB amp plates to produce strains AST-108, and AST-107, respectively. asd⁻ mutants complemented with pATIU6-derived plasmids were able to grow on LB agar and liquid media in the absence of DAP.

In a subsequent iteration, the ampicillin resistance gene (AmpR) from pATI-shTREX1 was replaced with a kanamycin resistance gene. This was accomplished by digestion of pATI-shTREX1 plasmid with HindIII followed by gel purification to remove the AmpR gene, PCR amplification of the kanamycin resistance (KanR) gene using primers APR-001 and APR-002 (SEQ ID NO:226 and SEQ ID NO:227, respectively), digestion with HindIII and ligation into the gel purified, digested pATIU6 plasmid.

In subsequent iterations, a single point mutation was introduced into the pATIKan plasmid at the pUC 19 origin of replication using the Q5® Site-Directed Mutagenesis Kit (New England Biolabs) and the primers APR-003 (SEQ ID NO:228) and APR-004 (SEQ ID NO:229) to change the nucleotide T at position 148 to a C. This mutation makes the origin of replication homologous to the pBR322 origin of replication in order to reduce the plasmid copy number.

Primer SEQ ID Description Sequence ID NO APR-001 Kan primerF AAAAAAGCTTGCAGCTCT 226 GGCCCGTG APR-002 Kan PrimerR AAAAAAGCTTTTAGAAAA 227 ACTCATCGAGCATCAAAT GA APR-003 pATI ori ACACTAGAAGgACAGTAT 228 T148CF TTGGTATCTG APR-004 pATI ori AGCCGTAGTTAGGCCACC 229 T148CR pATI2.0

A plasmid was designed and synthesized that contains the following features: a pBR322 origin of replication, an SV40 DNA nuclear targeting sequence (DTS), an rrnB terminator, a U6 promoter for driving expression of shRNAs followed by flanking restriction sites for cloning the promoter and shRNAs or microRNAs, the asd gene, an rrnG terminator, a kanamycin resistance gene flanked by HindIII sites for curing, and a multicloning site (SEQ ID NO:247). In addition, a plasmid was designed and synthesized for expression of two separate shRNA or microRNAs. This plasmid contains the following features: a pBR322 origin of replication, an SV40 DNA nuclear targeting sequence (DTS), an rrnB terminator, a U6 promoter for driving expression of shRNAs followed by flanking restriction sites for cloning the promoter and shRNAs or microRNAs, an H1 promoter for driving the expression of a 2^(nd) shRNA or microRNA, a 450 bp randomly generated stuffer sequence placed between the H1 and U6 promoters, the asd gene, an rrnG terminator, a kanamycin resistance gene flanked by HindIII sites for curing, and a multicloning site (SEQ ID NO:245).

Example 7 S. typhimurium Flagellin Knockout Strain Engineering by Deletion of the fliC and fljB Genes

In the example herein, S. typhimurium strains were engineered to lack both flagellin subunits fliC and fljB to reduce pro-inflammatory signaling. Deletions of fliC and fljB were sequentially engineered into the chromosome of the asd gene-deleted strain of YS1646 (AST-101).

Deletion of fliC

In this example, fliC was deleted from the chromosome of the AST-101 strain using modifications of the method of Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645 (2000)) as described in detail in Example 1 and schematically depicted in FIG. 4 . Synthetic fliC gene homology arm sequences were ordered that contained 224 and 245 bases of homologous sequence flanking the fliC gene, cloned into a plasmid called pSL0147 (SEQ ID NO:230). A kanamycin gene cassette flanked by cre/lox p sites then was cloned into pSL0147, the fliC gene knockout cassette was then PCR amplified with primer flic-1 (SEQ ID NO:232) and flic-2 (SEQ ID NO:233) and gel purified and introduced into the AST-101 strain carrying the temperature sensitive lambda red recombination plasmid pKD46 by electroporation. Electroporated cells were recovered in SOC+DAP medium and plated onto LB Agar plates supplemented with Kanamycin (20 μg/mL) and diaminopimelic acid (DAP, 50 μg/ml). Colonies were selected and screened for insertion of the knockout fragment by PCR using primers flic-3 (SEQ ID NO:234) and flic-4 (SEQ ID NO:235). pKD46 then was cured by culturing the selected kanamycin resistant strain at 42° C. and screening for loss of ampicillin resistance. The Kanamycin resistance marker then was cured by electroporation of a temperature sensitive plasmid expressing the Cre recombinase (pJW1680) and Amp^(R) colonies were selected at 30° C.; pJW168 was subsequently eliminated by growing cultures at 42° C. Selected fliC knockout clones were then tested for loss of kanamycin marker by PCR using primers flanking the sites of disruption (flic-3 and flic-4) and evaluation of the electrophoretic mobility on agarose gels.

Deletion of fljB

fljB was then deleted in the asd/fliC deleted YS1646 strain using modifications of the methods described above. Synthetic fljB gene homology arm sequences that contained 249 and 213 bases of the left hand and right hand sequence, respectively, flanking fljB gene, were synthesized and cloned into a plasmid called pSL0148 (SEQ ID NO:231). A kanamycin gene cassette flanked by cre/loxP sites then was cloned into pSL0148 and the fljB gene knockout cassette then was PCR amplified with primer fljb-1 (SEQ ID NO:236) and fljb-2 (SEQ ID NO:237) and gel purified and introduced into AST-101 carrying the temperature sensitive lambda red recombination plasmid pKD46 by electroporation. The kanamycin resistance gene then was cured by cre-mediated recombination as described above, and the temperature-sensitive plasmids were cured by growth at non-permissive temperature. The fliC and fljB gene knockout sequences were amplified by PCR using primers flic-3 and flic-4 or fljb-3 (SEQ ID NO:238) and fljb-4 (SEQ ID NO:239), and verified by DNA sequencing. This asd⁻/fliC⁻/fljB⁻ mutant derivative of YS1646 was designated AST-111.

Primer sequence information Primer SEQ name Primer sequence ID NO. flic-1 CGTTATCGGCAATCTGGAGGC 232 flic-2 CCAGCCCTTACAACAGTGGTC 233 flic-3 GTCTGTCAACAACTGGTCTAACGG 234 flic-4 AGACGGTCCTCATCCAGATAAGG 235 fljb-1 TTCCAGACGACAAGAGTATCGC 236 fljb-2 CCTTTAGGTTTATCCGAAGCCAGAATC 237 fljb-3 CACCAGGTTTTTCACGCTGC 238 fljb-4 ACACGCATTTACGCCTGTCG 239 In Vitro Characterization of Engineered S. typhimurium Flagellin Knockout Strain

The YS1646 derived asd⁻ mutant strain harboring the deletions of both fliC and fljB, herein referred to as AST-111 or ASD/FLG, was evaluated for swimming motility by spotting 10 microliters of overnight cultures onto swimming plates (LB containing 0.3% agar and 50 mg/mL DAP). While motility was observed for YS1646 and the asd deleted strain AST-101, no motility was evident with the asd/fliC/fljB-deleted strain AST-111. The AST-111 strain then was electroporated with pATIshTREX1 (a plasmid containing an asd gene and an shRNA targeting TREX1), to produce AST-112, and its growth rate in the absence of DAP was assessed. As shown in FIG. 5 , ASD/FLG (pATI-shTREX1) strain AST-112 was able to replicate in LB in the absence of supplemental DAP, and grew at a rate comparable to the asd strain containing pATIshTREX1 (AST-108). These data demonstrate that the elimination of flagellin does not decrease the fitness of S. typhimurium in vitro.

Elimination of flagellin subunits decreases pyroptosis in macrophages. To demonstrate this, 5×10⁵ mouse RAW-Dual™ macrophage cells (InvivoGen, San Diego, Ca.) were infected with the asd/fliC/fljB-deleted strain harboring a low copy shTREX1 plasmid, designated AST-118, or the asd deleted strain harboring the same plasmid (AST-117) at an MOI of approximately 100 in a gentamycin protection assay. After 24 hours of infection, culture supernatants were collected and assessed for lactate dehydrogenase release as a marker of cell death using a Pierce™ LDH Cytotoxicity Assay Kit (Thermo Fisher Scientific, Waltham, Ma.). AST-117 induced 75% maximal LDH release, while AST-118 induced 54% maximal LDH release, demonstrating that the deletion of the flagellin genes reduces the S. typhimurium-induced pyroptosis.

ASD/FLG Knockout Strain Containing shTrex1 Plasmid Demonstrates Enhanced Anti-Tumor Activity, Enhanced Interferon Gamma Responses, and Increased Tumor Colonization in Mice Compared to Parental asd Strain.

To assess the impact of the flagellin knockout strains administered in a murine model of colon carcinoma, 6-8 week-old female BALB/c mice (10 mice per group) were inoculated SC in the right flank with CT26 (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected with three weekly doses of 5×10⁶ CFUs of the ASD/FLG strain containing the pATIKan-shTREX1 plasmid (AST-113) or the ASD strain with the same pATIKan-shTREX1 plasmid (AST-110), and compared to PBS control. Six hours following the first IV dose, mice were bled, and plasma was collected and assessed for pro-inflammatory cytokines using the Mouse Inflammation Cytometric Bead Array kit and analyzed by FACS (BD Biosciences).

As shown in FIG. 6 , the AST-113 strain, incapable of making flagella and containing the pATIshTrex1 plasmid (ASD/FLG pATI-shTREX1), demonstrated enhanced tumor control compared to the parental ASD pATI-shTREX1 strain AST-110, and significant tumor control compared to the PBS control (54% TGI, p=0.02, day 17).

Comparing the levels of systemic serum cytokines at 6 hours post IV injection, the cytokines elicited by the AST-113 strain were comparable for TNF-α and IL-6 as compared to the parental AST-110 strain, capable of making flagella. The levels of the potent anti-tumor immune cytokine IFN-γ were significantly higher with AST-113 compared to AST-110, indicating that the flagellin deficient strain can provide for superior anti-tumor potency over the parental asd knockout strain (FIG. 7 ).

At 35 days post tumor implantation (12 days after the last dose of engineered Salmonella therapy), three mice per group were euthanized, and tumors were homogenized and plated on LB plates to enumerate the number of colony forming units (CFUs) per gram of tumor tissue as described above. As shown in FIG. 8 , the AST-113 strain, deleted of fliC and fljB and containing the pATIshTREX1 plasmid, was able to colonize tumors at least as well as the strain that only had the asd gene deletion and contained the same plasmid (AST-110). AST-113 colonized tumors with a mean of 1.2×10⁷ CFU per gram of tissue compared with a mean of 2.1×10⁶ CFU/g of tumor for AST-110, indicating that the absence of flagellin can lead to an increased tumor colonization by greater than 5 times that of strains with a functional flagella. Together, these data demonstrate that, contrary to the expectation from the art, not only is the flagella not required for tumor colonization, but its loss can enhance tumor colonization and anti-tumor immunity.

Example 8

S. typhimurium Engineered to Express cytoLLO for Enhanced Plasmid Delivery

In this example, the asd deleted strain of YS1646 described in Example 1 (AST-101) was further modified to express the listeriolysin O (LLO) protein lacking the signal sequence that accumulates in the cytoplasm of the Salmonella strain (referred to herein as cytoLLO). LLO is a cholesterol-dependent pore-forming cytolysin that is secreted from Listeria monocytogenes and mediates phagosomal escape of bacteria. A gene encoding LLO, with codons 2-24 deleted, was synthesized with codons optimized for expression in Salmonella. The sequence of the open reading frame of cytoLLO is in SEQ ID NO:240. The cytoLLO gene was placed under control of a promoter that induces transcription in S. typhimurium (SEQ ID NO: 241, reproduced below). The cytoLLO expression cassette was inserted in single copy into the knockout-out asd locus of the asd deleted strain AST-101 using modifications of the method of Datsenko and Wanner (Proc. Natl. Acad. Sci. USA (2000) 97:6640-6645), as described in Example 1.

Sequence of promoter driving expression of cytoLLO LLO promoter SEQ ID NO: 241 attatgtcttgacatgtagtgagtgggctggtataatgcagcaag

The asd deleted strain with the cytoLLO expression cassette inserted at the asd locus (referred to herein as ASD/LLO or AST-114) was further modified by electroporation with a pATI plasmid encoding an asd gene that allows the strain to grow in the absence of exogenous DAP and selects for plasmid maintenance, and also contains a U6 promoter driving expression of shTREX1 as described in Example 6 (referred to herein as ASD/LLO (pATI-shTREX1) or AST-115). As shown in FIG. 9 , the ASD/LLO (pATI-shTREX1) strain AST-115 grew at a comparable rate to the asd deleted strain containing the same plasmid (pATI-shTREX1), AST-110, demonstrating that the LLO knock-in does not impact bacterial fitness in vitro.

S. typhimurium Engineered to Produce cytoLLO Demonstrate Potent Anti-Tumor Activity

To determine whether the cytoLLO gene knock-in provided anti-tumor efficacy, the ASD/LLO (pATI-shTREX1) strain AST-115 was evaluated in a murine model of colon carcinoma. For this study, 6-8 week-old female BALB/c mice (8 mice per group) were inoculated SC in the right flank with CT26 (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected with a single dose of 5×10⁶ CFUs of AST-115, and compared to PBS control.

As shown in FIG. 10 , the addition of the cytoLLO gene into the asd⁻ strain ASD/LLO (pATI-shTREX1) demonstrated highly significant tumor control compared to PBS control (76% TGI, p=0.002, day 28), and comparable efficacy after a single dose to previous studies where the TREX1 shRNA plasmid containing strains were given at multiple doses. These data demonstrate the cytoLLO-mediated advantage of delivering more plasmid into the cytosol, resulting in greater gene knockdown, thereby improving the therapeutic efficacy of RNAi against targets such as TREX1.

Example 9 Adenosine Auxotrophic Strains of S. typhimurium

Strains provided herein are engineered to be auxotrophic for adenosine. As a result, they are attenuated in vivo because they are unable to replicate in the low adenosine concentrations of normal tissue, therefore colonization occurs primarily in the solid tumor microenvironment, where adenosine levels are high. The Salmonella strain YS1646 (AST-100) is a derivative of the wild type strain ATCC 14028, and was engineered to be auxotrophic for purine due to disruption of the purI gene (Low et al., (2004) Methods Mol. Med. 90:47-60). Subsequent analysis of the entire genome of YS1646 demonstrated that the purI gene (synonymous with purM) was not in fact deleted, but was instead disrupted by a chromosomal inversion (Broadway et al. (2014) J. Biotechnol. 192:177-178), and that the entire gene is still contained within two parts of the YS1646 chromosome that is flanked by insertion sequences (one of which has an active transposase). The presence of the complete genetic sequence of the purI gene disrupted by means of a chromosomal reengagement leaves open the possibility of reversion to a wild type gene. While it has previously been demonstrated that purine auxotrophy of YS1646 was stable after serial passage in vitro, it was not clear what the reversion rate is (Clairmont et al. (2000) J. Infect. Dis. 181:1996-2002).

It is shown herein that, when provided with adenosine, YS1646 is able to replicate in minimal medium; whereas the wild-type parental strain ATCC 14028 can grow in minimal media that is not supplemented with adenosine. YS1646 was grown overnight in LB medium washed with M9 minimal medium and diluted into M9 minimal media containing no adenosine, or increasing concentrations of adenosine. Growth was measured using a SpectraMax® M3 spectrophotometer (Molecular Devices) at 37° C., reading the OD₆₀₀ every 15 minutes.

As shown in FIG. 11 , strain YS1646 was able to replicate when adenosine was provided at concentrations ranging from 11 to 300 micromolar, but was completely unable to replicate in M9 alone or M9 supplemented with 130 nanomolar adenosine. These data demonstrate that purI mutants are able to replicate in concentrations of adenosine that are found in the tumor microenvironment, but not at concentrations found in normal tissues. Engineered adenosine auxotrophic strains exemplified herein include strains wherein all, or portions of the purI open reading frame are deleted from the chromosome to prevent reversion to wild-type. Such gene deletions can be achieved utilizing the lambda red system as described in Example 1.

Salmonella strains containing a purI disruption, further engineered to contain an asd gene deletion (ASD) as described in Example 1, or containing an asd gene deletion further engineered to have deletions of fliC and fljB (ASD/FLG), as described in Example 7, or asd⁻ mutants further engineered to express cytoLLO (ASD/LLO) as described in Example 8, and complemented with a low copy number plasmid (pATIlow) expressing asd as described in Example 6 (Strains AST-117, AST-118, and AST-119, respectively), were also evaluated for growth in M9 minimal media. The data in FIG. 12 show that each strain was able to replicate when adenosine was provided at concentrations ranging from 11 to 300 micromolar, but was completely unable to replicate in M9 alone or M9 supplemented with 130 nanomolar adenosine.

Example 10 Characterization and Use of the asd Gene Complementation System In Vitro Growth of Strains with asd Gene Complementation

To assess fitness of the bacterial strains containing plasmids, growth curves were performed in LB liquid media using a SpectraMax® plate reader at 37° C., reading the OD₆₀₀ every 15 minutes. As shown in FIG. 13 , strain YS1646 containing a low copy plasmid pEQU6-shTREX1 (AST-104) grew comparably to strain YS1646 that did not contain a plasmid (AST-100). An asd⁻ mutant strain harboring a high copy shTREX1 plasmid with an asd gene that can complement the asd deletion (AST-110) was able to replicate in LB in the absence of DAP, but grew slower than strain YS1646. An asd deleted strain containing an shTREX-1 expression plasmid with a low copy number origin of replication and an asd gene that can complement the asd deletion (pATIlow-shTREX1), strain AST-117, grew at a faster rate than AST-110. These data demonstrate that low copy number plasmids that complement the asd gene deletion are superior to high copy number plasmids, as they allow for more rapid replication rates of S. typhimurium in vitro.

Intracellular Growth of asd Complemented Strains

To measure fitness of the asd⁻ mutants complemented with asd on high and low copy plasmids, the ability of bacterial strains to replicate intracellularly in mouse tumor cell lines was assessed using a gentamycin protection assay. In this assay, mouse melanoma B16.F10 cells or mouse colon cancer CT26 cells were infected with asd⁻ mutant Salmonella strains containing plasmids that contain a complementary asd gene and have either a high copy origin of replication, AST-110 (ASD pATI-shTREX1), or a low copy origin of replication, AST-117 (ASD pATI low copy-shTREX1). Cells were infected at a multiplicity of approximately 5 bacteria per cell for 30 minutes, then cells were washed with PBS, and medium containing gentamicin was added to kill extracellular bacteria. Intracellular bacteria are not killed by gentamicin, as it cannot cross the cell membrane. At various time points after infection, cell monolayers were lysed by osmotic shock with water and the cell lysates were diluted and plated on LB agar to enumerate surviving colony forming units (CFU).

As shown in FIG. 14 , the asd⁻ mutant strain complemented with a high copy plasmid, AST-110, had an initial decline in CFUs, but was able to grow in B16.F10 cells but not in CT26 cells, demonstrating that the asd gene complementation system is sufficient to support growth inside mammalian tumor cells. The asd⁻ mutant strain containing the low copy plasmid, AST-117, was able to invade and replicate in both cell types, demonstrating that asd gene complementation on a low copy plasmid allows for robust asd⁻ mutant growth inside mammalian cells. The strain with a low copy plasmid replicated to higher numbers in both tumor cell types, compared to the strain with a high copy plasmid. This demonstrates that Salmonella strains with low copy plasmids have enhanced fitness over strains with high copy plasmids.

Plasmid Maintenance in Tumors Using asd Complementation System

In this example, CT26 tumor-bearing mice were treated with strain YS1646 containing a plasmid that expresses an shRNA targeting TREX1 (pEQU6-TREX1), strain AST-104, or an asd deleted strain of YS1646 containing a plasmid with a functional asd gene and an shRNA targeting TREX1 (pATI-shTREX1), strain AST-110. At 12 days after the final Salmonella injection, tumors were homogenized, and homogenates were serially diluted and plated on LB agar plates to enumerate the total number of CFUs present, or on LB plates containing kanamycin to enumerate the number of kanamycin resistant colonies.

As shown in FIG. 15 , S. typhimurium that did not have selective pressure to maintain the shRNA plasmid, AST-104, demonstrated plasmid loss, as the percent kanamycin resistant (KanR) colonies was less than 10%. The strain that used the asd gene complementation system for plasmid maintenance, AST-110, had nearly identical numbers of kanamycin resistant and kanamycin sensitive CFUs. These data demonstrate that the asd gene complementation system is sufficient to maintain the plasmid in the context of the tumor microenvironment in mice.

Enhanced Anti-Tumor Efficacy Using asd Complementation System

The asd complementation system is designed to prevent plasmid loss and potentiate the anti-tumor efficacy of the inhibitory RNA delivery by S. typhimurium strains in vivo. To test this, asd deleted strains containing shTREX1 plasmid (AST-110) or scrambled control (AST-109) that contain a functional asd gene cassette were compared to YS1646 containing pEQU6-shTREX1 (AST-104, a plasmid that lacks an asd gene cassette and therefore does not have a mechanism for plasmid maintenance) for anti-tumor efficacy in a murine colon carcinoma model. For this experiment, 6-8 week-old female BALB/c mice (8 mice per group) were inoculated SC in the right flank with CT26 (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected twice, on day 8 and day 18, with 5×10⁶ CFUs of AST-109 (ASD transformed with pATI-shScramble), AST-110 (ASD transformed with pATI-shTREX1), or AST-104 (YS1646 transformed with pEQU6-shTREX1) and compared to PBS control.

As shown in FIG. 16 , the YS1646 strain AST-104 demonstrated tumor control compared to PBS (70% TGI, day 28) despite its demonstrated plasmid loss over time. The asd⁻ strain containing the scramble control in a pATI plasmid with the asd gene complementation system (AST-109) demonstrated tumor control compared to PBS (51% TGI, day 25), indicating that maintained delivery of CpG plasmids stimulates an anti-tumor response. The asd⁻ strain containing plasmid with the asd gene complementation system and shTREX1 (AST-110) demonstrated the highest tumor growth inhibition compared to PBS (82% TGI, p=0.002, day 25). These data demonstrate that improved potency is achieved by preventing plasmid loss using the asd complementation system and delivery of shTREX1, as compared to YS1646 containing plasmids without gene complementation systems or shTREX1.

S. typhimurium Strains with Low Copy Plasmids Demonstrate Superior Anti-Tumor Efficacy and Tumor Colonization Compared to High Copy Plasmids

In order to compare the anti-tumor efficacy of the low copy shTREX1 plasmid with the asd complementation system, relative to the high copy shTREX1plasmid in a murine model of colon carcinoma, 6-8 week-old female BALB/c mice (10 mice per group) were inoculated SC in the right flank with CT26 (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected with two weekly doses of 5×10⁶ CFUs of AST-117 (ASD (pATI Low-shTREX1)) or AST-110 (ASD (pATI-shTREX1) and were compared to PBS injections as a negative control. As shown in FIG. 17 , the strain with the low copy plasmid, AST-117, demonstrated superior anti-tumor efficacy compared to the strain with the high copy plasmid, AST-110 (High: 59% TGI, Low: 79% TGI, p=0.042, day 25).

At the end of this tumor growth inhibition study, 4 mice from each group were euthanized, and tumors and spleens were homogenized as described above to evaluate tumor colonization and tumor to spleen colonization ratios. As shown in FIG. 18A, the strain containing the low copy plasmid, AST-117, colonized tumors at a level greater than 100 times higher than the strain with the high copy plasmid, AST-110. When the ratio of colonies recovered from tumor and spleen were calculated, AST-117 had a greater than 10-fold higher tumor to spleen colonization ratio compared to AST-110 (FIG. 18B), demonstrating that the strain with the low copy plasmid had greater specificity for tumor colonization than the strain with the high copy plasmid.

These data demonstrate a previously unknown attribute that S typhimurium engineered to deliver plasmids encoding interfering RNAs have improved tumor colonizing capabilities and anti-tumor efficacy when the plasmids have low copy number origins of replication.

Example 11 Engineering of an Autolytic S. typhimurium Strain for Delivery of RNAi

As described above, the asd gene in S. typhimurium encodes aspartate semialdehyde dehydrogenase. Deletion of this gene renders the bacteria auxotrophic for diaminopimelic acid (DAP) when grown in vitro or in vivo. This example employs an asd deletion strain (described in Example 1) that is auxotrophic for DAP and contains a plasmid suitable for delivery of RNAi that does not contain an asd-complementing gene so that the strain is defective for replication in vivo. This strain is propagated in vitro in the presence of DAP and grows normally, and then is administered as an immunotherapeutic agent to mammalian hosts where DAP is not present, which results in autolysis of the bacteria. Autolytic strains are able to invade host cells, but are not able to replicate due to the absence of DAP in mammalian tissues; this combination of attributes allows for RNAi-mediated gene knockdown and increased safety relative to replicating strains.

In this example, the asd deleted strain of YS1646 (AST-101, described in Example 1) was further modified to express cytoLLO to generate strain AST-114 (described in Example 8), was electroporated to contain a plasmid encoding ARI-203 (a microRNA targeting TREX1), to make strain AST-120 (ASD/LLO (pEQU6-miTREX1)). When this strain is introduced into tumor bearing mice, the bacteria are taken up by host cells and enter the Salmonella containing vacuole (SCV). In this environment, the lack of DAP prevents replication, and result in lysis of the bacteria in the SCV. Lysis of AST-120 allows for release of the plasmid, and the accumulated cytoLLO that form pores in the cholesterol-containing SVC membrane, resulting in efficient delivery of the plasmid into the cytosol of the host cell.

The ability of the autolytic strain AST-120, to replicate in LB in the presence or absence of DAP was assessed using a SpectraMax® M3 spectrophotometer (Molecular Devices) at 37° C., reading the OD₆₀₀ every 15 minutes. As shown in FIG. 19 , AST-120 is able to grow robustly in LB supplemented with 50 μg/mL DAP, but cannot replicate in LB alone.

Increased Attenuation of Autolytic S. typhimurium in Mice To determine whether the autolytic strain AST-120, engineered to deliver cytoLLO and a microRNA targeting TREX1, was attenuated for virulence, a median lethal dose (LD₅₀) study was performed. Increasing doses of AST-120, ranging from 1×10⁶ to 5×10⁷ CFUs, were administered IV to C57BL/6 mice (a strain of mouse that is highly sensitive to LPS). After IV administration, AST-120 was well tolerated at all doses with transient weight loss observed after a single dose. A second dose was administered 7 days after the first dose and one mouse out of four, at the highest dose level (5×10⁷ CFUs), was found moribund and required euthanasia. All other mice administered AST-120 experienced transient weight loss, but recovered. These data indicate that the LD₅₀ for the autolytic strain of S. typhimurium delivering a micro-RNA targeting TREX1 (AST-120) is greater than 5×10⁷ CFUs. The LD₅₀ for the VNP20009 strain is known to be approximately 5×10⁶ CFUs in C57BL/6 mice (Lee et al. (2000) International Journal of Toxicology 19:19-25), demonstrating that AST-120 is at least 10-fold attenuated compared to VNP20009.

Antitumor Activity of Autolytic S. typhimurium

To determine whether the autolytic strain AST-120, engineered to deliver cytoLLO and a microRNA targeting TREX1, was able to provide an anti-tumor response, 6-8 week-old female BALB/c mice (10 mice per group) were inoculated SC in the right flank with CT26 (2×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected with a single dose of 5×10⁶ CFUs of the autolytic strain AST-120 (ASD/LLO (pEQU6-miTREX1)) and compared to mice treated with PBS as a control. As shown in FIG. 20 , an antitumor response was detected after only a single dose, compared to animals treated with PBS alone (52.4% TGI, p=0.02, day 17). Together, these data demonstrate that S. typhimurium engineered to be autolytic by means of DAP auxotrophy and engineered to contain a plasmid for delivery of RNAi targeting TREX1, are exquisitely attenuated and can elicit an anti-tumor response.

Example 12 Exemplary Strains Engineered for Increased Tolerability adrA or csgD Deletion

In this example, a live attenuated strain of Salmonella typhimurium that contains a purI deletion, an msbB deletion, an asd gene deletion, and is engineered to deliver plasmids encoding interfering RNA, is further modified to delete adrA, a gene required for Salmonella typhimurium biofilm formation. Salmonella that cannot form biofilms are taken up more rapidly by host phagocytic cells and are cleared more rapidly. This increase in intracellular localization enhances the effectiveness of plasmid delivery and gene knockdown by RNA interference. The increased clearance rate from tumors/tissues increases the tolerability of the therapy, and the lack of biofilm formation prevents colonization of prosthetics and gall bladders in patients. In another example, a live attenuated strain of Salmonella typhimurium that contains a purI deletion, an msbB deletion, an asd gene deletion and is engineered to deliver plasmids encoding interfering RNA, is further modified to delete csgD. This gene is responsible for activation of adrA, and also induces expression of the curli fimbriae, a TLR2 agonist. Loss of csgD also prevents biofilm formation, with the added benefit of inhibiting TLR2 activation, thereby further reducing the bacterial virulence and enhancing delivery of RNAi.

pagP Deletion

In this example, a live attenuated strain of S. typhimurium that contains a purI deletion, an msbB deletion, and an asd gene deletion, and is engineered to deliver plasmids encoding interfering RNA, is further modified to delete pagP. The pagP gene is induced during the infectious life cycle of S. typhimurium and encodes an enzyme that palmitoylates lipid A. In wild type S. typhimurium, expression of pagP results in a lipid A that is hepta-acylated. In an msbB⁻ mutant, in which the terminal acyl chain of the lipid A cannot be added, the expression of pagP results in a hexa-acylated LPS. Hexa-acylated LPS has been shown to be the most pro-inflammatory. In this example, a strain deleted of pagP and msbB can produce only penta-acylated LPS, allowing for lower pro-inflammatory cytokines, enhanced tolerability, and increased adaptive immunity when the bacteria are engineered to deliver interfering RNAs.

hilA deletion

In this example, a live attenuated strain of Salmonella typhimurium that contains a purI deletion, an msbB deletion, and an asd gene deletion, and is engineered to deliver plasmids encoding interfering RNA, is further modified to delete hilA. hilA is a regulatory gene that is required for expression of the Salmonella pathogenicity island 1 (SPI-1)-associated type 3 secretion system (T3SS). This secretion system is responsible for injecting effector proteins into the cytosol of non-phagocytic host cells, such as epithelial cells, that cause the uptake of modified S. typhimurium. The SPI-1 T3SS has been shown to be essential for crossing the gut epithelial layer, but is dispensable for infection when bacteria are injected parenterally. The injection of some proteins and the needle complex itself can also induce inflammasome activation and pyroptosis of phagocytic cells. This pro-inflammatory cell death can limit the initiation of a robust adaptive immune response by directly inducing the death of antigen-presenting cells (APCs), as well as modifying the cytokine milieu to prevent the generation of memory T-cells. In this example, the additional deletion of the hilA gene from a therapeutic Salmonella typhimurium strain that is administered either intravenously or intratumorally focuses the Salmonella typhimurium infection towards phagocytic cells that do not require the SPI-1 T3SS for uptake, and then prolongs the longevity of these phagocytic cells. The hilA mutation reduces the quantity of pro-inflammatory cytokines, increasing the tolerability of the therapy, as well as the quality of the adaptive immune response.

Example 13 HilA Deletion Mutants Grow Normally In Vitro

The hilA gene was deleted from the YS1646 strain of S. typhimurium with the asd gene deleted, and the YS1646 strain deleted of asd, and flagellin genes fljB and fliC, using the lambda-derived Red recombination system as described in Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645(2000)) to make the strains HilA/ASD and HilA/FLG/ASD, respectively. These strains were then electroporated with a plasmid containing a functional asd gene (to complement the deleted asd gene and to ensure plasmid maintenance in vivo) and a eukaryotic expression cassette containing the U6 promoter driving expression of a microRNA targeting murine TREX-1 (pATI-miTREX1). The in vitro growth rates of strains HilA/ASD (pATI-miTREX1) and HilA/FLG/ASD (pATI-miTREX1) were then determined and compared to the strains ASD (pATI-miTREX1) and YS1646 at 37° C. in LB broth, as measured by OD₆₀₀ using a SpectraMax® 96-well plate reader (Molecular devices). Each modified strain grew at a rate comparable to the parental YS1646 strain in vitro, indicating that the hilA deletion does not reduce the fitness of the bacteria in vitro.

Example 14 HilA Deletion Mutants Induce Less Cell Death in Human Monocytic Cells

To assess whether a hilA deletion mutant induced less pyroptosis than strains capable of producing SPI-1, human THP-1 monocytic cells were infected with a multiplicity of infection (MOI) of 1000 bacteria with strains YS1646, ASD (pATI-miTREX1), FLG/ASD (pATI-miTREX1), and HilA/ASD (pATI-miTREX1). After 1 hour of infection, extracellular bacteria were removed and the media was replaced with media containing gentamycin at 100 μg/mL to kill extracellular bacteria. At 4 hours post infection, cells were harvested and THP-1 cell viability was assessed using CellTiter-Glo (Promega) reagent uptake and measuring luminescence using a SpectraMax® 96-well plate reader (Molecular devices). While infection with YS1646 resulted in 86% cell death, infection with HilA/ASD (pATI-miTREX1) only resulted in 46% cell death. The % dead cells for ASD (pATI-miTREX1) and FLG/ASD (pATI-miTREX1) strains demonstrated intermediate phenotypes with 77% and 68% cell death, respectively. These data demonstrate that hilA deleted strains induce less cell death in human monocytic cells than S. typhimurium strains capable of expressing SPI-1.

Example 15 HilA Deletion Mutants have Reduced Capacity to Infect Human Epithelial Cells

HeLa cells were infected with a multiplicity of infection of 500 bacteria with strains YS1646, ASD (pATI-miTREX1), FLG/ASD (pATI-miTREX1), and HilA/ASD (pATI-miTREX1). After 1 hour, extracellular bacteria were removed and the media was replaced with media containing gentamycin at 100 μg/mL to kill extracellular bacteria. At 4 hours post infection, cells were harvested and lysed by osmotic shock, and the number of viable colony forming units of bacteria were enumerating by serial dilution and plating on LB agar plates. 4.6×10³ CFUs per well were recovered with YS1646, and only 2.0×10² CFUs were recovered with the HilA/ASD (pATI-miTREX1) strain. Strains ASD (pATI-miTREX1) and FLG/ASD (pATI-miTREX1) demonstrated intermediate phenotypes with 8.0×10² CFUs and 6.0×10² CFUs recovered, respectively. These data demonstrate that hilA deleted strains induce less uptake in human epithelial cells than S. typhimurium strains capable of expressing SPI-1.

Example 16 PagP Deletion Mutants have Penta-Acylated LPS and Induce Reduced Inflammatory Cytokines

The pagP gene was deleted from the asd gene-deleted strain of S. typhimurium YS1646 (which contains a purI/M and msbB deletion), using the lambda-derived Red recombination system as described in Datsenko and Wanner (Proc. Natl. Acad. Sci. USA 97:6640-6645 (2000)) to generate the strain PagP/ASD. This strain was then electroporated with a plasmid containing a functional asd gene (to complement the deleted asd gene and to ensure plasmid maintenance in vivo) and a eukaryotic expression cassette containing the U6 promoter driving expression of a microRNA targeting murine TREX-1 (pATI-miTREX1) to generate the strain PagP/ASD (pATI-miTREX1). The Lipid A was then extracted from this strain and evaluated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and compared to wild-type S. typhimurium strain ATCC 14028, strain YS1646 (which is deleted for msbB and purM), and strain YS1646 deleted for the asd gene and complimented with the pATI-miTREX1 plasmid. Wild-type Salmonella had a minor lipid A peak with a mass of 2034, and a major peak with a mass of 1796, corresponding to the hepta-acylated and hexa-acylated species, respectively, due to the presence of functional msbB and purM genes. The msbB deleted strains YS1646 and ASD (pATI-miTREX1) had major peaks at 1828 and 1585, corresponding to a mixture of hexa-acylated and penta-acylated LPS. The msbB and pagP deleted strain, PagP/ASD (pATI-TREX1) had only a single peak with a mass of 1585. These data demonstrate that deletion of pagP prevents palmitoylation of the LPS, thereby restricting it to a single penta-acylated species.

To determine whether the penta-acylated LPS from the pagP mutant strains reduced TLR-4 signaling, 4 μg of purified LPS from the strains described above were added to THP-1 human monocytic cells, and the supernatants were evaluated 24 hours later for the presence of inflammatory cytokines using a cytometric bead array (CBA) kit (BD Biosciences). The LPS from the PagP⁻ strain induced ¼ the amount of TNF-alpha compared to wild-type LPS, and 7-fold less IL-6 than wild-type. The pagP⁻ mutant LPS induced 22-fold less IL-6 than YS1646, demonstrating that the penta-acylated LPS species from a pagP⁻ mutant is significantly less inflammatory in human cells, and indicating that the pagP⁻ mutant would be better tolerated in humans.

Example 17 FLG, HilA and PagP Deletion Mutants are More Attenuated than Strain YS1646 in Mice

To determine whether the modified strains described above are more attenuated than strain YS1646, a median lethal dose (LD₅₀) study was conducted. C57BL/6 mice were injected intravenously with increasing concentrations of strains YS1646, FLG/ASD (pATI-TREX1), HilA/ASD (pATI-TREX1), or PagP/ASD (pATI-TREX1). The LD₅₀ for strain YS1646 was found to be 1.6×10⁶ CFUs, which is consistent with published reports of this strain. The LD₅₀ for the HilA/ASD (pATI-TREX1) strain was determined to be 5.3×10⁶ CFUs, demonstrating a 3-fold reduction in virulence. The LD₅₀ for the PagP/ASD (pATI-TREX1) strain was determined to be 6.9×10⁶ CFUs, demonstrating a 4-fold reduction in virulence. The LD₅₀ for the FLG/ASD (pATI-TREX1) strain was determined to be >7×10⁶ CFUs, demonstrating a >4.4-fold reduction in virulence compared to strain YS1646. These data indicate that the genetic modifications described above reduce the virulence of the S. typhimurium therapy and will lead to increased tolerability in humans. In the Phase I clinical trial of VNP20009 (Toso et al. (2002) J. Clin. Oncol. 20(1):142-152), the presence of the bacteria in patients' tumors was only partially observed at the two highest doses tested, 3E8 CFU/m² (33% presence), and 1E9 CFU/m² (50% presence), indicating that the tolerable dose of VNP20009 was too low to achieve colonization. By improving the tolerability of the strains through the modifications described above, higher doses can be administered than VNP20009. This improves both the percentage of patients that will have their tumors colonized, and the level of therapeutic colonization per tumor.

Example 18 HilA Deletion Mutants Demonstrate Significant Anti-Tumor Activity in Mice, and Comparable Activity to the fljB/fliC Deletion Mutants

The hilA⁻ mutation should prevent upregulation of the T3SS, and prevent pyroptotic cell death of infected macrophages. This should enhance tolerability and anti-tumor efficacy of the plasmid-containing target strains in vivo. To test this, ΔhilA/Δasd strains containing the miTREX1 plasmid (HilA/ASD (pATI-miTrex1)) or vehicle control were compared to ΔfljB/ΔfliC/Δasd strains containing the miTREX1 (FLG/ASD (pATI-miTrex1)) plasmid for tumor efficacy in a murine colon carcinoma model. 6-8 week-old female C57BL/6 mice (9 mice per group) were inoculated S.C. in the right flank with MC38 cells (5×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were I.V. injected on day 8 with 3×10⁵ CFUs of strains HilA/ASD (pATI-miTrex1), FLG/ASD (pATI-miTrex1), or PBS vehicle control. Body weights and tumors were measured twice weekly. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula ½(length×width). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations.

The data demonstrate that the HilA/ASD (pATI-miTrex1) strain induces potent tumor control compared to PBS (83.6% TGI, day 25), including 1/9 complete tumor regressions. These data were comparable to those observed with the FLG/ASD (pATI-miTrex1) strain compared to PBS (82.8% TGI, day 25). Thus, the ΔhilA strain provides comparable or greater potency in a murine tumor model as the ΔfljB/ΔfliC strain.

Example 19 HilA Deletion Mutants Demonstrate Significantly Lower Systemic Cytokines than the Parental VNP20009 Strain, and Enhanced Colonization Compared to the fljB/fliC Deletion Mutants

To test the impact of the ΔhilA/Δasd and ΔfljB/ΔfliC/Δasd strains on tumor colonization and tolerability, compared to the parental VNP20009 strain, these strains, containing the miTREX1 plasmid, were evaluated in a murine colon carcinoma model. 6-8 week-old female C57BL/6 mice (3 mice per group) were inoculated S.C. in the right flank with MC38 cells (5×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were I.V. injected on day 8 with 3×10⁵ and 1×10⁵ CFUs of HilA/ASD (pATI-miTrex1), FLG/ASD (pATI-miTrex1), VNP20009 or PBS vehicle control. Mice were bled 2 hours post-dosing, and serum assessed for systemic cytokines by a mouse inflammation cytometric bead array (BD Biosciences) on a flow cytometer (Novocyte). On day 3 post I.V. dosing, mice were sacrificed, and the tumors, spleens and livers were harvested and weighed. Tissues were homogenized in 10 mL sterile PBS (M tubes, GentleMACs™, Miltenyi Biotec), then 10-fold serial dilutions were performed and plated on LB (Luria Broth) agar plates containing LB+kanamycin (Sigma). The following day, colony forming units (CFUs) were counted and total CFUs were assessed per gram of tissue.

Serum cytokine IL-6 levels in mice have been shown to be the most accurate correlate of clinical tolerability. The IL-6 levels from VNP20009 at the 3e5 CFU dose averaged 11,755 pg/mL, compared to the baseline 18 pg/mL of PBS control. The HilA/ASD (pATI-miTrex1) and FLG/ASD (pATI-miTrex1) IL-6 levels at the 3e5 CFU dose were both significantly lower than the VNP20009 levels (3,570 pg/mL and 3,850 pg/mL, respectively). These data demonstrate the significantly enhanced tolerability of the mutant strains compared to the parental VNP20009 strain. Comparing the colonization of tumors, spleens and livers 3 days post I.V. dosing of 1e5 CFU, the overall colonization of the spleens between HilA/ASD (pATI-miTrex1) and FLG/ASD (pATI-miTrex1) was comparable (HilA: 2.1e4 CFU/g, vs. FLG: 1.2e4 CFU/g), while the FLG/ASD (pATI-miTrex1) strain had somewhat lower colonization in the liver (HilA: 7.4e3 CFU/g, vs. FLG: 1.5e3 CFU/g). The tumor colonization of the HilA/ASD (pATI-miTrex1) strain was shown to be an average of 2.6e4 CFU/g, which was significantly higher than the undetectable levels found in the FLG/ASD (pATI-miTrex1) tumors at the same time point. These data demonstrate the high degree of tolerability and enhanced tumor colonization properties of the ΔhilA/Δasd strain.

Example 20 S. typhimurium Immune Modulator Strains Demonstrate Expression of Heterologous Proteins in Human Monocytes

As described above, the hilA gene and flagellin genes fljB and fliC were deleted from the YS1646 strain of S. typhimurium with the asd gene deleted, generating the strains HilA/ASD and FLG/ASD, respectively. In addition, the FLG/ASD strain was further modified to express the listeriolysin O (LLO) protein lacking the signal sequence (cytoLLO) that accumulates in the cytoplasm of the Salmonella strain (FLG/ASD/cLLO). These strains were electroporated with a plasmid containing an expression cassette for the EF1c promoter and the murine cytokine IL-2 (muIL-2). In addition, the FLG/ASD strain was electroporated with an expression plasmid for IL-156 as a control for a non-cognate cytokine. Additional constructs were created using the CMV promoter.

To determine whether these strains containing expression plasmids could infect human monocytes and induce the production of murine IL-2, THP-1 human monocytic cells were plated at 50,000 cells/well in RPMI (Corning)+10% Nu Serum (Gibco) one day prior to infection. The cells were infected at an MOI of 50 for one hour in RPMI, then washed 3 times with PBS, and resuspended in RPMI+100 μg/ml Gentamycin (Sigma). Supernatants were collected 48 hours later from a 96 well plate and assessed for the concentration of murine IL-2 by ELISA (R&D Systems). The concentration of IL-2 detected in the FLG/ASD-IL15δ control wells was found to be very low as expected, and likely reflective of some cross-reactivity to endogenous human IL-2 (6.52 pg/mL). In contrast, the FLG/ASD-IL-2 strain induced an average of 35.1 pg/ml IL-2, and an even higher concentration of IL-2 was measured with the FLG/ASD/cLLO strain, 59.8 pg/mL. The highest levels were detected in the HilA/ASD-IL-2 strain, 103.4 pg/mL. These data demonstrate the feasibility of expressing and secreting functional heterologous proteins, such as IL-2, from the S. typhimurium immune modulator platform strains.

Example 21 Cell Infection with ΔhilA Mutant Leads to Less Human Epithelial Cell Infection

To demonstrate that hilA deleted S. typhimurium strains are reduced in their ability to infect epithelial cells, HeLa cervical carcinoma cells were infected with the following S. typhimurium strains: YS1646, YS1646 Δasd and YS1646 Δasd/ΔhilA, containing plasmids encoding a functional asd gene for plasmid maintenance. 1×10⁶ HeLa cells were placed in a 24-well dish with DMEM and 10% FBS. Cells were infected with log-phase cultures of S. typhimurium for 1 hour, then the cells were washed with PBS and the media was replaced with media containing 50 μg/mL gentamicin to kill extracellular bacteria. After 4 hours, the HeLa cell monolayers were washed with PBS and lysed with 1% Triton X 100 lysis buffer to release intracellular bacteria. The lysates were serially diluted and plated on LB agar plates to quantify the number of intracellular bacteria. The strain with the hilA deletion had a 90% reduction in recovered CFUs compared to the strains with a functional hilA gene, demonstrating that deletion of hilA significantly decreases S. typhimurium infection of epithelial-derived cells.

Example 22 Cell Infection with ΔhilA or ΔfljB/ΔfliC Mutants Leads to Less Pyroptosis in Human Macrophages

To demonstrate that ΔhilA or ΔfljB/ΔfliC S. typhimurium strains are reduced in their ability cause cell death in macrophages, THP-1 human macrophage cells were infected with the following S. typhimurium strains: YS1646, YS1646 Δasd, YS1646 Δasd/ΔfljB/ΔfliC, and YS1646 Δasd/ΔhilA, containing plasmids encoding a functional asd gene to ensure plasmid maintenance. 5×10⁴ cells were placed in a 96-well dish with DMEM and 10% FBS. Cells were infected with washed log-phase cultures of S. typhimurium for 1 hour at an MOI of 100 CFUs per cell, then the cells were washed with PBS, and the media was replaced with media containing 50 μg/mL gentamicin to kill extracellular bacteria, and 50 ng/mL of interferon gamma. After 24 hours, the THP-1 cells were stained with CellTiter-Glo® reagent (Promega), and the percentage of viable cells was determined using a luminescent cell viability assay using a SpectraMax® plate reader to quantify the luminescence. The cells infected with the hilA deletion strain had approximately 72% viable cells, whereas the YS1646-infected cells had only 38% viability, demonstrating that deletion of hilA prevents cell death of human macrophages. Cells infected with the plasmid-containing strains YS1646 Δasd and YS1646 Δasd/ΔfljB/ΔfliC had 40% and 51% viability, respectively, indicating that the deletion of the flagellin genes also prevented cell death of human macrophages.

Example 23 Infection of Human Macrophages with an Immunostimulatory S. typhimurium Strain Containing a Plasmid Encoding IL-2 Expression Cassette Leads to Secretion of IL-2

Human THP-1 macrophages were infected with the following S. typhimurium strains: YS1646 Δasd/ΔfljB/ΔfliC, YS1646 Δasd-cytoLLO, and YS1646 Δasd/ΔhilA, containing plasmids encoding an expression cassette for murine IL-2 under a eukaryotic promoter, and a functional asd gene to ensure plasmid maintenance. 5×10⁴ cells were placed in a 96-well dish with DMEM and 10% FBS. Cells were infected with washed log-phase cultures of S. typhimurium for 1 hour at an MOI of 50 CFUs per cell, then the cells were washed with PBS and the media was replaced with media containing 50 μg/mL gentamicin to kill extracellular bacteria. After 48 hours, the cellular supernatants were removed and tested for murine IL-2 using an R&D Systems™ Mouse IL-2 Quantikine ELISA Kit. The remaining cells were stained with CellTiter-Glo® reagent (Promega), and the percentage of viable cells was determined using a luminescent cell viability assay using a SpectraMax® plate reader to quantify the luminescence. The YS1646 Δasd/ΔfljB/ΔfliC, YS1646 Δasd-cytoLLO, and YS1646 Δasd/ΔhilA strains, containing plasmids encoding an expression cassette for murine IL-2, expressed 35 pg/mL, 60 pg/mL, and 103 pg/mL of IL-2, respectively.

Example 24 S. typhimurium Strains Expressing Murine IL-2 Demonstrate Potent Tumor Growth Inhibition In Vivo

The immunostimulatory S. typhimurium strains containing deletions in hilA or the flagellin genes fljB and fliC in the YS1646 strain of S. typhimurium were combined with the asd gene deletion to form the strains YS1646 Δasd/ΔhilA and YS1646 Δasd/ΔfljB/ΔfliC, respectively. These strains were electroporated with a plasmid containing an expression cassette for the EF1c promoter and the murine cytokine IL-2.

To show that the S. typhimurium strains containing the IL-2 expression plasmids induce anti-tumor efficacy, the Δasd/ΔhilA strains containing the muIL-2 plasmid, or the Δasd/ΔfljB/ΔfliC strains containing the muIL-2 plasmid, were compared to vehicle control. 6-8 week-old female C57BL/6 mice (5 mice per group) were inoculated S.C. in the right flank with MC38 cells (5×10⁵ cells in 100 μL PBS). Mice bearing established flank tumors were IV injected on day 8 with 5×10⁵ CFUs of Δasd/ΔhilA (pATI-muIL-2), Δasd/ΔfljB/ΔfliC (pATI-muIL-2), or PBS vehicle control. Body weights and tumors were measured twice weekly. Tumor measurements were performed using electronic calipers (Fowler, Newton, Mass.). Tumor volume was calculated using the modified ellipsoid formula, ½(length×width²). Mice were euthanized when tumor size reached >20% of body weight or became necrotic, as per IACUC regulations.

The experiment demonstrated that the Δasd/ΔhilA (pATI-muIL-2) strain elicited significant tumor control compared to PBS (P=0.003, day 21). These data were comparable to that observed with the Δasd/ΔfljB/ΔfliC (pATI-muIL-2) strain, which also demonstrated significant tumor growth inhibition compared to PBS (P=0.005, day 21). Thus, both strains demonstrate the ability of expressed IL-2 to potently inhibit tumor growth inhibition in a model of colorectal carcinoma.

Example 25 pagP⁻, fljB⁻/fliC⁻, and pagP⁻/fljB⁻/fliC⁻ Strains Demonstrate Significantly Higher Viability in Human Serum Compared to VNP20009 (YS1646)

As described herein, VNP20009 (YS1646) exhibits limited tumor colonization in humans after systemic administration. It is shown herein that VNP20009 is inactivated by complement factors in human blood. To demonstrate this, strains YS1646 and E. coli D10B were compared to exemplary immunostimulatory bacteria provided herein that contain additional mutations that alter the surface of the bacteria. These strains were YS1646 (pagP⁻), YS1646 (fljB⁻/fliC⁻), and YS1646 (pagP⁻/fljB⁻/fliC⁻). These three strains, in addition to YS1646 and E. coli D10B cultures, were incubated with serum or heat-inactivated (HI) serum from either pooled mouse blood or pooled healthy human donors (n=3), for 3 hours at 37° C. After incubation with serum, bacteria were serially diluted and plated on LB agar plates, and the colony forming units (CFUs) were measured.

In mouse serum, all strains remained 100% viable and were completely resistant to complement inactivation. In human serum, all strains were 100% viable in the heat-inactivated serum. The E. coli D10B strain was completely eliminated after 3 hours in whole human serum. The YS1646 strain exhibited only 6.37% of live colonies, demonstrating that tumor colonization of the YS1646 clinical strain was limited due to complement inactivation in human blood. For the YS1646 (fljB⁻/fliC⁻) strain, 31.47% of live colonies remained, and for the YS1646 (pagP⁻) strain, 72.9% of live colonies remained, after incubation with human serum for 3 hours. The combined YS1646 (pagP⁻/fljB⁻/fliC⁻) strain was completely resistant to complement in human serum.

These data explain why VNP20009 had very low tumor colonization when systemically administered. It is shown herein that VNP20009 (YS1646) is highly sensitive to complement inactivation in human serum, but not mouse serum. These data explain why limited tumor colonization was observed in humans, while mouse tumors were colonized at a high level. The fljB/fliC or pagP deletions, or the combination of these mutations, partially or completely rescues this phenotype. Thus, the enhanced stability observed in human serum with the fljB/fliC, pagP, or pagP/fljB/fliC deletion strains provides for increased human tumor colonization.

These data and other provided herein (see, e.g., Examples 7, 16 and 17, above) show that deletion of the flagella and/or pagP increases tumor colonization, improves tolerability, and increases the anti-tumor activity of the immunostimulatory bacteria. Example 16 demonstrates that LPS from immunostimulatory bacteria that are pagP⁻ induced 22-fold less IL-6 than LPS from YS1646, and therefore pagP⁻ bacteria are less inflammatory in human cells. Example 17 demonstrates that each and all of FLG, HilA and PagP deletion mutants are more attenuated than YS1646.

Immunostimulatory bacteria, such as Salmonella strains, including wild-type strains, that are one or both of flagellin and pagP⁻ exhibit properties that increase tumor/tumor microenvironment colonization and increase anti-tumor activity. Such strains can be used to deliver a therapeutic payload, such as an immunotherapeutic product and/or other anti-tumor product, and also can include modifications that improve therapeutic properties, such as deletion of hilA, and/or msbB, adenosine auxotrophy, and other properties as described elsewhere herein. The resulting strains are more effectively targeted to the tumor/tumor microenvironment, by virtue of the modifications that alter infectivity, toxicity to certain cells, and nutritional requirements, such as auxotrophy for purines, that are provided in the tumor environment.

Example 26 fljB⁻/fliC⁻ Immunostimulatory Bacterial Strain Demonstrates Tumor Myeloid Cell-Specific Colonization In Vivo

The asd and flagellin (fljB/fliC) genes were deleted from strain YS1646, which is purI⁻/msbB⁻, using the lambda-derived Red recombination system as described previously (see, Datsenko and Wanner (2000) Proc. Natl. Acad. Sci. USA 97:6640-6645), to generate the strain YS1646 ΔFLG/ΔASD. Strain YS1646 ΔFLG/ΔASD was then transformed by electroporation with the bacterial plasmid pRPSM-mCherry, containing 1) a functional asd expression cassette to complement the chromosomal deletion of asd for in vivo plasmid maintenance, and 2) a constitutive mCherry expression cassette under control of the bacterial rpsm promoter (rpsm-mCherry). Bacterial colonies transformed with this plasmid were visibly red in color, due to expression of the mCherry red fluorescent protein. To evaluate tumor colonization, the transformed bacterial strain (YS1646 ΔFLG/ΔASD (pRPSM-mCherry)) was tested in vivo in a murine colon carcinoma model. 6-8 week-old female C57BL/6 mice (3 mice per group) were inoculated subcutaneously in the right flank with MC38 cells (5×10⁵ cells in 100 μL PBS). Mice bearing large, established flank tumors were intravenously injected with 1×10⁶ CFUs of YS1646 ΔFLG/ΔASD (pRPSM-mCherry). Tumors were harvested 3 days later and dissociated into a single cell suspension (Miltenyi Biotec). Cells were stained with Zombie Aqua™ fixable viability dye (BioLegend), which penetrates dead, but not live, cells. The cells were incubated with the following antibodies: Brilliant Violet 510™ anti-mouse CD45 (clone 30-F11, BioLegend); Brilliant Violet 421™ anti-mouse CD8a (clone 53-6.7, BioLegend); PE anti-mouse CD3ε (clone 145-2C11, BioLegend); FITC anti-mouse CD4 (clone RM4-5, BioLegend); PE/Cy7 anti-mouse/human CD11b (clone M1/70, BioLegend); Brilliant Violet 785™ anti-mouse Ly6C (clone HK1.4, BioLegend); Brilliant Violet 605™ anti-mouse Ly6G (clone 1A8, BioLegend); APC anti-mouse F4/80 (clone BM8, BioLegend); and PercP/Cy5.5 anti-mouse CD24 (clone M1/69, Biolegend). The cells were then sorted by flow cytometry (Novocyte) using the various surface markers and mCherry⁺ (PE Texas Red), to determine/localize bacterial uptake by the harvested cells.

CD45⁻ cells, which include stromal and tumor cells, demonstrated no detectable bacterial colonization, with 0.076% cells being positive for mCherry, compared to a background staining level of 0.067%. CD45⁺ tumor-infiltrating myeloid cells were positive for mCherry, with 7.27% of monocytes, 3.33% of dendritic cells (DCs), and 8.96% of macrophages being positive for mCherry, indicating uptake of the YS1646 ΔFLG/ΔASD (pRPSM-mCherry) bacteria. A control strain, containing intact flagella, was tested in parallel. Unlike the ΔFLG strain, the flagellin⁺ control strain infected CD45⁻ cells, with 0.36% of CD45⁻ cells being positive for mCherry, which was 5.37-fold greater than background staining (0.067%). The flagellin⁺ control strain also infected CD45⁺ myeloid populations, with 5.71% of monocytes, 5.56% of DCs, and 9.52% of macrophages being positive for mCherry. These data indicate that flagella knockout strains accumulate in the myeloid cell populations of the tumor, but not in the tumor or stromal cells, whereas strains with intact flagella infect all cell types. Thus, flagella knockout strains demonstrate tumor myeloid-specific colonization in vivo.

Example 27 Flagella Knockout (ΔfljB/ΔfliC) and ΔpagP Strains Demonstrate Increased Tolerability and Decreased Immunogenicity In Vivo

The pagP gene was deleted from the S. typhimurium strains YS1646 ΔASD and YS1646 ΔFLG/ΔASD, generating the strains YS1646 ΔPagP/ΔASD and YS1646 ΔPagP/ΔFLG/ΔASD, respectively. Strains YS1646 ΔFLG/ΔASD, YS1646 ΔPagP/ΔASD, and YS1646 ΔPagP/ΔFLG/ΔASD were transformed by electroporation with plasmids encoding the asd gene, as well as a eukaryotic expression cassette encoding murine IL-2 (muIL-2). To test the tolerability of these strains in vivo, an LD₅₀ study was performed in 6-8 week old female BALB/c mice. The mice were intravenously injected with 3×10⁵, 1×10⁶, 3×10⁶, 1×10⁷, or 3×10⁷ CFUs of strains YS1646, YS1646 ΔFLG/ΔASD (muIL-2), YS1646 ΔPagP/ΔASD (muIL-2), or YS1646 ΔPagP/ΔFLG/ΔASD (muIL-2). The mice were then monitored for morbidity and mortality, and the LD₅₀ values were calculated. The results are shown in the table below.

Bacterial Strain LD₅₀ (CFUs) YS1646 7.24 × 10⁶ YS1646 ΔFLG/ΔASD (muIL-2) 2.07 × 10⁷ YS1646 ΔPagP/ΔASD (muIL-2) 1.39 × 10⁷ YS1646 ΔPagP/ΔFLG/ΔASD (muIL-2) Not calculated

The LD₅₀ values for the YS1646 ΔFLG/ΔASD (muIL-2) and YS1646 ΔPagP/ΔASD (muIL-2) strains were higher than the LD₅₀ value for the parental YS1646 strain, indicating that the tolerability of the flagellin⁻ and pagP deletion mutants, expressing murine IL-2, was higher in vivo. The LD₅₀ for strain YS1646 ΔPagP/ΔFLG/ΔASD (muIL-2) was not calculated, as no animals died during the duration of the study, but was greater than 6.2×10⁷ CFUs, representing a near 10-fold improvement in the tolerability, compared to the parental YS1646 strain.

To compare the immunogenicity of the different bacterial strains, mice that survived the 3×10⁶ CFU dose (N=5, except YS1646, where N=4) were bled at day 40 post intravenous dosing, and anti-Salmonella serum antibodies were titered. Sera from mice treated with the various mutant bacterial strains, and from control mice, were seeded in a 96-well PCR plate and serially diluted in PBS. Cultures of the S. typhimurium strains containing the pRPSM-mCherry plasmid were spun down and washed, then resuspended in flow-cytometry fixation buffer. For the assay, 25 μl of the mCherry⁺ bacterial cultures, containing 1×10⁶ CFUs, were added to the sera and incubated for 25 minutes at room temperature. Following incubation, the bacterial samples were centrifuged and washed twice with PBS by spinning them at 4000 RPM for 5 min, and then resuspended in PBS containing a secondary goat anti-mouse Fc Alexa Fluor® 488 antibody (1/400 dilution from stock), and incubated for 25 minutes at room temperature in the dark. The samples were then washed three times with PBS by spinning them at 4000 RPM for 5 min, resuspended in PBS, and analyzed by flow cytometry (Novocyte). The results showed that the mice injected with parental strain YS1646 had the highest serum antibody titers, with an average mean fluorescence intensity (MFI) of 29,196±20,730. Sera from mice injected with strain YS1646 ΔFLG/ΔASD (muIL-2) had an MFI of 7,941±9,290; sera from mice injected with strain YS1646 ΔPagP/ΔASD (muIL-2) had an MFI of 3,454±3,860; and sera from mice injected with strain YS1646 ΔPagP/ΔFLG/ΔASD (muIL-2), had the lowest serum antibody titers, with an MFI of 2,295±2,444. The data demonstrate that deletion of the genes encoding the flagella (fljB/fliC) or pagP result in strains with decreased immunogenicity, and that the combination of mutations (ΔPagP/ΔFLG) further decreases the immunogenicity, compared to the parental strain without the deletions.

Overall, the data demonstrate the improved tolerability and decreased immunogenicity of the ΔFLG and ΔPagP strains, with the ΔPagP/ΔFLG/ΔASD strain demonstrating the most favorable tolerability and lowest immunogenicity.

Since modifications will be apparent to those of skill in the art, it is intended that this invention be limited only by the scope of the appended claims. 

What is claimed:
 1. A method of treatment of cancer that comprises a solid tumor or a hematological malignancy in a subject, comprising administering an immunostimulatory bacterium, wherein: the immunostimulatory bacterium comprises a plasmid that encodes an anti-cancer therapeutic product; the genome of the immunostimulatory bacterium is modified so that, compared to the bacterium without the genome modifications, the bacterium has increased ability to infect tumor-resident immune cells, and has reduced ability to infect or does not infect epithelial cells; and the anti-cancer therapeutic product is expressed under the control of one or more eukaryotic regulatory sequences, whereby the product is expressed in the tumor-resident immune cells in the subject.
 2. The method of claim 1, wherein the immunostimulatory bacterium is administered systemically.
 3. The method of claim 1, wherein the immunostimulatory bacterium is administered intra-tumorally or is administered intra-peritoneally.
 4. The method of claim 1, wherein the subject is a human.
 5. The method of claim 1, wherein the cancer comprises a solid tumor.
 6. The method of claim 1, wherein the treatment comprises combination therapy in which a second anti-cancer agent or treatment is administered.
 7. The method of claim 6, wherein the second anti-cancer agent or treatment is an immunotherapy.
 8. The method of claim 6, wherein the second anti-cancer agent or treatment comprises oncolytic virus therapy, or immunotherapy to inhibit an immune checkpoint.
 9. The method of claim 6, wherein the second anti-cancer agent or treatment is an immunotherapy that comprises administration of an anti-PD-1, or an anti-PD-L1, or an anti-CTLA-4, or an anti-IL-6, or an anti-VEGF, or an anti-VEGFR2, or an anti-CD47 antibody, or antigen-binding fragments thereof.
 10. The method of claim 1, wherein the cancer is selected from among leukemia, lymphoma, gastric cancer, and cancer of the breast, heart, lung, bile duct, small intestine, colon, spleen, kidney, bladder, head and neck, colorectum, ovary, prostate, brain, pancreas, skin, bone, bone marrow, blood, thymus, uterus, testicles, cervix, and liver.
 11. The method of claim 1, wherein the immunostimulatory bacterium is a Salmonella species.
 12. The method of claim 11, wherein the immunostimulatory bacterium is a Salmonella typhimurium strain.
 13. The method of claim 12, wherein the Salmonella typhimurium strain is derived from a wild-type Salmonella typhimurium strain having all of the identifying characteristics of the strain deposited under ATCC accession no. 14028, or is the strain deposited under ATCC accession no.
 14028. 14. The method of claim 1, wherein: the eukaryotic regulatory sequences comprise a eukaryotic promoter; the genome of the immunostimulatory bacterium is modified, whereby the bacterium lacks flagella to thereby reduce infection of epithelial cells and increase infection of tumor-resident immune cells relative to the wild-type bacterium; and the wild-type bacterium has flagella.
 15. The method of claim 1, wherein the genome of the immunostimulatory bacterium is modified, whereby the bacterium is msbB⁻/pagP⁻.
 16. The method of claim 14, wherein the genome of the immunostimulatory bacterium is modified, whereby the bacterium is msbB⁻/pagP⁻.
 17. The method of claim 14, wherein the immunostimulatory bacterium is fliC⁻/fljB⁻, whereby the bacterium is flagellin⁻.
 18. The method of claim 1, wherein: the anti-cancer therapeutic product is an immunostimulatory protein; and the immunostimulatory protein, when expressed in a mammalian subject, confers or contributes to anti-tumor immunity in the tumor microenvironment.
 19. The method of claim 1, wherein: the immunostimulatory bacterium is a Salmonella species; the immunostimulatory bacterium is an adenosine auxotroph; the immunostimulatory bacterium is flagellin⁻ (fliC⁻/fljB⁻); and the anti-cancer therapeutic product encoded on the plasmid is expressed under the control of eukaryotic regulatory sequences.
 20. The method of claim 19, wherein the nucleic acid encoding the anti-cancer therapeutic product on the plasmid is operatively linked to nucleic acid encoding a secretory signal, whereby, upon expression in a host, the product is secreted.
 21. The method of claim 1, wherein the genome of the immunostimulatory bacterium is modified, whereby the bacterium does not express functional endogenous aspartate-semialdehyde dehydrogenase (asd).
 22. The method of claim 21, wherein the plasmid encodes asd.
 23. The method of claim 1, wherein the immunostimulatory bacterium is auxotrophic for adenosine, or is auxotrophic for adenosine and adenine.
 24. The method of claim 1, wherein the plasmid is present in a copy number of less than
 150. 25. The method of claim 18, wherein the immunostimulatory protein that confers or contributes to anti-tumor immunity in the tumor microenvironment is a cytokine or a chemokine.
 26. The method of claim 18, wherein the immunostimulatory protein that confers or contributes to anti-tumor immunity in the tumor microenvironment is selected from among one or more of: IL-2, IL-7, IL-12p70 (IL-12p40+IL-12p35), IL-15, IL-2 that has attenuated binding to IL-2Ra, IL-15/IL-15R alpha chain complex, IL-18, IL-21, IL-23, IL-36γ, IL-2 that is modified so that it does not bind to IL-2Ra, CXCL9, CXCL10, CXCL11, interferon-α, interferon-β, interferon-γ, CCL3, CCL4, CCL5, proteins that are involved in or that effect or potentiate the recruitment and/or persistence of T cells, CD40, CD40 ligand (CD40L), CD28, OX40, OX40 ligand (OX40L), 4-1BB, 4-1BB ligand (4-1BBL), members of the B7-CD28 family, CD47 antagonists, TGF-beta polypeptide antagonists, and members of the tumor necrosis factor receptor (TNFR) superfamily.
 27. The method of claim 1, wherein the anti-cancer therapeutic product is an antibody or an antigen-binding fragment thereof.
 28. The method of claim 1, wherein the anti-cancer therapeutic product is an antibody or an antigen-binding fragment thereof that is an antagonist of PD-1, PD-L1, CTLA-4, VEGF, VEGFR2, CD47, or IL-6.
 29. The method of claim 1, wherein the anti-cancer therapeutic product is a monovalent or monospecific antibody derivative that contains either or both the variable heavy chain and the variable light chain, or contains antigen-binding fragments of an antibody, but lacks an Fc portion.
 30. The method of claim 1, wherein the anti-cancer therapeutic product is a bi-specific antibody or an antigen-binding portion thereof.
 31. The method of claim 1, wherein the anti-cancer therapeutic product is an antibody or a portion thereof that is a dual-affinity re-targeting (DART) antibody.
 32. The method of claim 1, wherein the anti-cancer therapeutic product is an antibody or an antigen-binding portion thereof that is a tandem scFv, whereby the tandem scFv is a bi-specific T-cell engager.
 33. The method of claim 1, wherein the anti-cancer therapeutic product is an antibody or an antigen-binding portion thereof that is a diabody, a single-chain diabody (scDb), a Fab, a Fab′, a single-chain Fab (scFab), an scFv, an Fv fragment, a dAb, or a nanobody.
 34. The method of claim 1, wherein the anti-cancer therapeutic product is a cytotoxin.
 35. The method of claim 1, wherein the anti-cancer therapeutic product is a tumor antigen or a tumor neoantigen.
 36. The method of claim 1, wherein the anti-cancer therapeutic product is expressed under control of an RNA polymerase II promoter that is a viral promoter or a mammalian RNA polymerase II promoter.
 37. The method of claim 36, wherein the promoter is selected from among a cytomegalovirus (CMV) promoter, an SV40 promoter, an Epstein-Barr virus (EBV) promoter, a herpes virus promoter, an adenovirus promoter, an elongation factor-1 alpha (EF-1 alpha) promoter, a UBC promoter, a PGK promoter, a CAGG promoter, an EIF4A1 promoter, a CBA (chicken beta actin) promoter, an MND promoter, a CD68 promoter, a CAG promoter, and a GAPDH promoter.
 38. The method of claim 1, wherein the eukaryotic regulatory sequences comprise a terminator and/or promoters selected from among SV40, hGH, BGH, chicken beta-globulin, and rbGlob (rabbit globulin) genes.
 39. The method of claim 1, wherein the immunostimulatory bacterium is a strain of Salmonella, Shigella, E. coli, Bifidobacteriae, Rickettsia, Vibrio, Listeria, Klebsiella, Bordetella, Neisseria, Aeromonas, Francisella, Cholera, Corynebacterium, Citrobacter, Chlamydia, Haemophilus, Brucella, Mycobacterium, Mycoplasma, Legionella, Rhodococcus, Pseudomonas, Helicobacter, Bacillus, or Erysipelothrix, or an attenuated strain thereof or a modified strain thereof of any of the preceding list of bacterial strains.
 40. The method of claim 18, wherein the immunostimulatory bacterium is a strain of Salmonella.
 41. The method of claim 40, wherein the immunostimulatory bacterium is a Salmonella typhimurium strain.
 42. The method of claim 41, wherein: the immunostimulatory bacterium is derived from a Salmonella typhimurium strain selected from among strains designated as AST-100, VNP20009, YS1646 (ATCC #202165), RE88, SL7207, χ8429, χ8431, and χ8468.
 43. The method of claim 41, wherein the immunostimulatory bacterium is derived from a wild-type strain of Salmonella typhimurium.
 44. The method of claim 43, wherein the wild-type strain of Salmonella typhimurium is ATCC
 14028. 45. The method of claim 1, wherein the plasmid comprises nucleic acid encoding a second anti-cancer therapeutic product, wherein different promoters and terminators control expression of each therapeutic product.
 46. The method of claim 1, wherein the plasmid that encodes the anti-cancer therapeutic product comprises a construct that includes one or more of an enhancer, a promoter, an internal ribosome entry site (IRES), the open reading frame encoding the therapeutic product, and a polyA tail.
 47. A method of treatment of cancer, comprising administering an immunostimulatory bacterium to a subject with cancer, wherein: the immunostimulatory bacterium comprises a plasmid that encodes a therapeutic product under the control of a eukaryotic promoter; the immunostimulatory bacterium comprises one or more genome modification(s), whereby the bacterium has penta-acylated lipopolysaccharide (LPS); and the immunostimulatory bacterium lacks flagella, wherein the wild-type bacterium comprises flagella.
 48. The method of claim 47, wherein the therapeutic product is a cytokine.
 49. The method of claim 47, wherein the immunostimulatory bacterium is a Salmonella species or strain.
 50. The method of claim 48, wherein the immunostimulatory bacterium is pagP⁻/msbB⁻, whereby the bacterium has penta-acylated LPS.
 51. The method of claim 49, wherein the immunostimulatory bacterium is pagP⁻/msbB⁻, whereby the bacterium has penta-acylated LPS.
 52. The method of claim 48, wherein the cytokine is IL-15/IL-15R alpha chain complex.
 53. The method of claim 11, wherein the immunostimulatory bacterium comprises genome modifications, whereby TLR2/4 signaling is reduced.
 54. The method of claim 47, wherein the immunostimulatory bacterium is an adenosine auxotroph.
 55. The method of claim 54, wherein the immunostimulatory bacterium is a Salmonella species or strain.
 56. The method of claim 55, wherein the immunostimulatory bacterium is csgD⁻.
 57. The method of claim 55, wherein the encoded therapeutic product is a cytokine.
 58. The method of claim 56, wherein the encoded therapeutic product is a cytokine.
 59. The method of claim 55, wherein the encoded therapeutic product is a cytokine that is IL-15 or is IL-15/IL-15R alpha chain complex.
 60. The method of claim 47, wherein the plasmid comprises nucleic acid encoding Rck protein. 